/* Whiteboard — finance & quant interview lab.
   Direction: paper whiteboard. Graph-paper ground, ruled index cards, marker-red traps, teal insights.
   Dark mode = blackboard. */

:root {
  --paper: #f4efe3;
  --paper2: #ebe4d2;
  --card: #fffdf8;
  --ink: #15213b;
  --ink2: #3b4763;
  --ink3: #667089;
  --rule: rgba(21, 33, 59, .14);
  --rule2: rgba(21, 33, 59, .3);
  --grid: rgba(21, 33, 59, .05);
  --trap: #c63a24;
  --trapbg: #fbe8e3;
  --ins: #0a6f7a;
  --insbg: #ddf0ef;
  --hl: #ffe27a;
  --ok: #2a7a4b;
  --okbg: #e1f1e7;
  --warn: #9a6200;
  --warnbg: #fdf0d2;
  --blue: #2b59c3;
  --lines: rgba(56, 108, 200, .26);
  --margin: rgba(214, 70, 52, .55);
  --shadow: 3px 3px 0 var(--rule);
  --shadow-lg: 6px 6px 0 var(--rule);
  --f-display: "Iowan Old Style", "Palatino Linotype", Palatino, "Book Antiqua", Georgia, serif;
  --f-body: "Segoe UI Variable Text", "Segoe UI", system-ui, -apple-system, Roboto, sans-serif;
  --f-mono: "Cascadia Mono", "Cascadia Code", Consolas, "SF Mono", Menlo, monospace;
  --r: 6px;
  --pad: clamp(16px, 4vw, 40px);
  color-scheme: light;
}
[data-theme="dark"] {
  --paper: #0c1322;
  --paper2: #111a2e;
  --card: #141d33;
  --ink: #e8ecf6;
  --ink2: #bcc6dc;
  --ink3: #8d9ab8;
  --rule: rgba(255, 255, 255, .12);
  --rule2: rgba(255, 255, 255, .26);
  --grid: rgba(255, 255, 255, .035);
  --trap: #ff8670;
  --trapbg: rgba(255, 134, 112, .12);
  --ins: #55d6cb;
  --insbg: rgba(85, 214, 203, .1);
  --hl: rgba(255, 214, 90, .3);
  --ok: #67d391;
  --okbg: rgba(103, 211, 145, .12);
  --warn: #f2c25b;
  --warnbg: rgba(242, 194, 91, .12);
  --blue: #86a8ff;
  --lines: rgba(134, 168, 255, .16);
  --margin: rgba(255, 134, 112, .45);
  --shadow: 3px 3px 0 rgba(0, 0, 0, .35);
  --shadow-lg: 6px 6px 0 rgba(0, 0, 0, .35);
  color-scheme: dark;
}

*, *::before, *::after { box-sizing: border-box; }
html { scroll-behavior: smooth; -webkit-text-size-adjust: 100%; }
@media (prefers-reduced-motion: reduce) { html { scroll-behavior: auto; } * { animation: none !important; transition: none !important; } }
body {
  margin: 0;
  background-color: var(--paper);
  background-image:
    linear-gradient(var(--grid) 1px, transparent 1px),
    linear-gradient(90deg, var(--grid) 1px, transparent 1px);
  background-size: 28px 28px;
  color: var(--ink);
  font: 400 1.0625rem/1.62 var(--f-body);
  min-height: 100vh;
}
a { color: var(--ins); text-underline-offset: 3px; }
a:hover { color: var(--ink); }
:focus-visible { outline: 3px solid var(--blue); outline-offset: 2px; border-radius: 3px; }
h1, h2, h3, h4 { font-family: var(--f-display); line-height: 1.15; margin: 0; letter-spacing: -.01em; }
p { margin: 0 0 1em; }
code { font-family: var(--f-mono); font-size: .9em; background: var(--paper2); padding: .1em .35em; border-radius: 3px; }
.muted { color: var(--ink3); }
.warn { color: var(--warn); }
.row { display: flex; flex-wrap: wrap; gap: .6rem .8rem; align-items: center; margin: .7rem 0; }
.skip { position: absolute; left: -999px; top: 8px; background: var(--ink); color: var(--paper); padding: .5rem 1rem; z-index: 100; }
.skip:focus { left: 8px; }
[hidden] { display: none !important; }
.hl { background: linear-gradient(transparent 58%, var(--hl) 58%); padding: 0 .12em; }
.mono { font-family: var(--f-mono); }

/* ------------------------------------------------------------------ math */
math { font-family: "Cambria Math", "STIX Two Math", "Latin Modern Math", "Noto Sans Math", serif; font-size: 1.12em; }
.eq { margin: .9rem 0; padding: .7rem 1rem; background: var(--card); border: 1px solid var(--rule); border-left: 4px solid var(--blue); border-radius: var(--r); overflow-x: auto; text-align: center; }
.eq math { font-size: 1.32em; }

/* ------------------------------------------------------------------ top bar */
.top { position: sticky; top: 0; z-index: 50; background: color-mix(in srgb, var(--paper) 92%, transparent); backdrop-filter: blur(6px); border-bottom: 1.5px solid var(--ink); }
.top-in { max-width: 1180px; margin: 0 auto; padding: .55rem var(--pad); display: flex; align-items: center; gap: 1.2rem; flex-wrap: wrap; }
.brand { font: italic 700 1.55rem/1 var(--f-display); color: var(--ink); text-decoration: none; display: flex; align-items: baseline; gap: .1rem; }
.brand i { color: var(--trap); font-style: normal; }
.nav { display: flex; gap: .15rem; flex-wrap: wrap; margin-left: auto; align-items: center; }
.nav a { color: var(--ink2); text-decoration: none; font-weight: 600; font-size: .92rem; padding: .35rem .7rem; border-radius: 4px; border: 1.5px solid transparent; }
.nav a:hover { background: var(--paper2); color: var(--ink); }
.nav a[aria-current="page"] { border-color: var(--ink); background: var(--card); color: var(--ink); box-shadow: 2px 2px 0 var(--rule2); }
.nav .count { display: inline-block; min-width: 1.35em; padding: 0 .35em; margin-left: .3em; background: var(--trap); color: #fff; border-radius: 99px; font-size: .75rem; text-align: center; font-weight: 700; }
.icon-btn { background: none; border: 1.5px solid var(--rule2); color: var(--ink); width: 2.1rem; height: 2.1rem; border-radius: 50%; cursor: pointer; font-size: 1rem; }
.icon-btn:hover { border-color: var(--ink); background: var(--paper2); }

.wrap { max-width: 1180px; margin: 0 auto; padding: 0 var(--pad); }
main { padding-bottom: 5rem; outline: none; }
.foot { border-top: 1px solid var(--rule); padding: 1.5rem var(--pad); text-align: center; color: var(--ink3); font-size: .85rem; }

/* ------------------------------------------------------------------ buttons & controls */
.btn { font: 600 .95rem/1 var(--f-body); padding: .7rem 1.1rem; border-radius: 5px; border: 1.5px solid var(--ink); background: var(--card); color: var(--ink); cursor: pointer; box-shadow: 2px 2px 0 var(--ink); transition: transform .08s, box-shadow .08s, background .15s; text-decoration: none; display: inline-block; }
.btn:hover { transform: translate(-1px, -1px); box-shadow: 3px 3px 0 var(--ink); }
.btn:active { transform: translate(1px, 1px); box-shadow: 0 0 0 var(--ink); }
.btn.primary { background: var(--ink); color: var(--paper); }
.btn.ghost { box-shadow: none; border-color: var(--rule2); background: transparent; }
.btn.ghost:hover { border-color: var(--ink); background: var(--card); transform: none; box-shadow: none; }
.btn.sm { padding: .45rem .75rem; font-size: .85rem; }
.btn.trap { background: var(--trap); border-color: var(--trap); color: #fff; box-shadow: 2px 2px 0 var(--ink); }
.btn:disabled { opacity: .45; cursor: not-allowed; transform: none; box-shadow: none; }
.ans { font: 600 1.05rem var(--f-mono); padding: .65rem .8rem; border: 1.5px solid var(--ink); background: var(--card); color: var(--ink); border-radius: 5px; width: 12rem; max-width: 100%; }
.ans-area { width: 100%; font: 1rem/1.5 var(--f-body); padding: .75rem .9rem; border: 1.5px solid var(--rule2); background: var(--card); color: var(--ink); border-radius: 5px; resize: vertical; }
.ans-area:focus, .ans:focus { border-color: var(--ink); }
.unit { color: var(--ink3); font-family: var(--f-mono); }
select { font: inherit; padding: .4rem .6rem; background: var(--card); color: var(--ink); border: 1.5px solid var(--rule2); border-radius: 5px; }

.ctl { display: block; min-width: 0; }
.ctl-l { display: flex; justify-content: space-between; gap: .6rem; font-size: .85rem; font-weight: 600; color: var(--ink2); margin-bottom: .15rem; }
.ctl-v { font-family: var(--f-mono); color: var(--ink); font-weight: 700; }
.ctl-h { font-size: .78rem; color: var(--ink3); display: block; margin-top: .1rem; }
.ctl-grid { display: grid; grid-template-columns: repeat(auto-fit, minmax(210px, 1fr)); gap: .8rem 1.4rem; margin: .4rem 0 1rem; }
input[type=range] { -webkit-appearance: none; appearance: none; width: 100%; height: 22px; background: transparent; --p: 50%; cursor: pointer; }
input[type=range]::-webkit-slider-runnable-track { height: 5px; border-radius: 3px; background: linear-gradient(90deg, var(--ink) var(--p), var(--rule2) var(--p)); }
input[type=range]::-moz-range-track { height: 5px; border-radius: 3px; background: var(--rule2); }
input[type=range]::-moz-range-progress { height: 5px; border-radius: 3px; background: var(--ink); }
input[type=range]::-webkit-slider-thumb { -webkit-appearance: none; width: 18px; height: 18px; margin-top: -7px; border-radius: 50%; background: var(--card); border: 2.5px solid var(--ink); box-shadow: 1px 1px 0 var(--ink); }
input[type=range]::-moz-range-thumb { width: 14px; height: 14px; border-radius: 50%; background: var(--card); border: 2.5px solid var(--ink); }
input[type=range]:disabled { opacity: .5; cursor: default; }

.seg { display: inline-flex; flex-wrap: wrap; border: 1.5px solid var(--ink); border-radius: 5px; overflow: hidden; background: var(--card); }
.seg button { font: 600 .85rem var(--f-body); padding: .45rem .8rem; background: transparent; color: var(--ink2); border: 0; border-right: 1px solid var(--rule2); cursor: pointer; }
.seg button:last-child { border-right: 0; }
.seg button[aria-pressed="true"] { background: var(--ink); color: var(--paper); }
.seg button:hover:not([aria-pressed="true"]) { background: var(--paper2); }

.stats { display: flex; flex-wrap: wrap; gap: .6rem; margin: .6rem 0; }
.stat { background: var(--card); border: 1px solid var(--rule2); border-radius: var(--r); padding: .45rem .8rem; min-width: 7.5rem; }
.stat-l { display: block; font-size: .72rem; text-transform: uppercase; letter-spacing: .06em; color: var(--ink3); font-weight: 600; }
.stat-v { font: 700 1.2rem var(--f-mono); }
.stat.trap .stat-v { color: var(--trap); }
.stat.ins .stat-v { color: var(--ins); }
.stat.ok .stat-v { color: var(--ok); }

/* ------------------------------------------------------------------ chart parts */
svg.plot { width: 100%; height: auto; display: block; overflow: visible; }
svg .grid { stroke: var(--rule); stroke-width: 1; }
svg .axis { stroke: var(--ink2); stroke-width: 1.5; }
svg .tick { font: 11px var(--f-mono); fill: var(--ink3); }
svg .axlab { font: 600 11.5px var(--f-body); fill: var(--ink2); }
svg .ln { fill: none; stroke: var(--ink); stroke-width: 2; stroke-linejoin: round; stroke-linecap: round; }
svg .ln.trap { stroke: var(--trap); } svg .ln.ins { stroke: var(--ins); } svg .ln.blue { stroke: var(--blue); }
svg .ln.dash { stroke-dasharray: 6 5; } svg .ln.thin { stroke-width: 1.2; } svg .ln.faint { stroke: var(--ink3); stroke-width: 1.2; opacity: .6; }
svg .ar { fill: var(--ink); opacity: .12; stroke: none; }
svg .ar.trap { fill: var(--trap); opacity: .18; } svg .ar.ins { fill: var(--ins); opacity: .2; } svg .ar.blue { fill: var(--blue); opacity: .18; }
svg .dt { fill: var(--ink); } svg .dt.trap { fill: var(--trap); } svg .dt.ins { fill: var(--ins); } svg .dt.ring { fill: var(--card); stroke: var(--ink); stroke-width: 2; }
svg .tx { font: 600 12px var(--f-body); fill: var(--ink2); } svg .tx.trap { fill: var(--trap); } svg .tx.ins { fill: var(--ins); } svg .tx.big { font-size: 15px; } svg .tx.blue { fill: var(--blue); }
svg .bar { fill: var(--ink); } svg .bar.trap { fill: var(--trap); } svg .bar.ins { fill: var(--ins); } svg .bar.soft { fill: var(--ink3); opacity: .45; } svg .bar.ok { fill: var(--ok); }

/* ------------------------------------------------------------------ home */
.hero { padding: clamp(2rem, 6vw, 4.2rem) 0 1.5rem; display: grid; gap: 1.2rem; }
.eyebrow { font: 700 .78rem var(--f-body); letter-spacing: .14em; text-transform: uppercase; color: var(--trap); }
.hero h1 { font-size: clamp(2.5rem, 7vw, 5.2rem); font-weight: 800; max-width: 15ch; }
.hero h1 em { font-style: italic; background: linear-gradient(transparent 62%, var(--hl) 62%); }
.hero .lede { font-size: clamp(1.1rem, 2.2vw, 1.35rem); max-width: 46rem; color: var(--ink2); }
.hero .cta { display: flex; gap: .8rem; flex-wrap: wrap; margin-top: .4rem; }

.sec { margin-top: clamp(2.2rem, 5vw, 3.6rem); }
.sec-h { display: flex; align-items: baseline; gap: .8rem; flex-wrap: wrap; margin-bottom: 1rem; }
.sec-h h2 { font-size: clamp(1.5rem, 3vw, 2rem); }
.sec-h p { margin: 0; color: var(--ink3); }

.qcards { display: grid; grid-template-columns: repeat(auto-fit, minmax(290px, 1fr)); gap: 1.4rem; }
.qcard { position: relative; background: var(--card); border: 1.5px solid var(--ink); border-radius: var(--r); padding: 2.6rem 1.2rem 1.1rem 3.1rem; box-shadow: var(--shadow-lg);
  background-image: repeating-linear-gradient(to bottom, transparent 0, transparent 31px, var(--lines) 31px, var(--lines) 32px);
  background-position: 0 2.2rem; background-repeat: repeat-y; }
.qcard::before { content: ""; position: absolute; left: 2.3rem; top: 0; bottom: 0; width: 2px; background: var(--margin); }
.qcard::after { content: ""; position: absolute; left: 0; right: 0; top: 2.2rem; height: 2px; background: var(--margin); opacity: .6; }
.qcard-tag { position: absolute; left: 3.1rem; top: .55rem; font: 700 .72rem var(--f-body); letter-spacing: .12em; text-transform: uppercase; color: var(--trap); }
.qcard-q { font: 500 1.18rem/32px var(--f-display); color: var(--ink); position: relative; z-index: 1; }
.qcard-q b { font-weight: 800; text-decoration: underline; text-decoration-thickness: 2px; text-underline-offset: 4px; }
.qcard-q .ask { color: var(--trap); font-weight: 700; }
.qcards .qcard:nth-child(1) { transform: rotate(-.7deg); } .qcards .qcard:nth-child(2) { transform: rotate(.5deg); } .qcards .qcard:nth-child(3) { transform: rotate(-.3deg); }
.qwrap { display: flex; flex-direction: column; gap: .8rem; }
.qwrap .need { font-size: .9rem; color: var(--ink2); }
.qwrap .need b { color: var(--ink); }
.stamp { display: inline-block; font: 800 .72rem var(--f-body); letter-spacing: .1em; text-transform: uppercase; color: var(--ink); border: 2px solid var(--ink); border-radius: 3px; padding: .1rem .4rem; transform: rotate(-2deg); opacity: .85; }
.chips { display: flex; flex-wrap: wrap; gap: .35rem; margin: .2rem 0; }
.chip { font: 600 .78rem var(--f-body); padding: .15rem .55rem; border-radius: 99px; border: 1.5px solid var(--rule2); color: var(--ink2); background: var(--card); text-decoration: none; }
a.chip:hover { border-color: var(--ink); color: var(--ink); }
.chip.on { background: var(--ink); color: var(--paper); border-color: var(--ink); }

.next { display: grid; grid-template-columns: repeat(auto-fit, minmax(240px, 1fr)); gap: 1rem; }
.panel { background: var(--card); border: 1.5px solid var(--ink); border-radius: var(--r); padding: 1.1rem 1.2rem; box-shadow: var(--shadow); }
.panel h3 { font-size: 1.15rem; margin-bottom: .35rem; }
.panel .k { font: 700 .72rem var(--f-body); letter-spacing: .12em; text-transform: uppercase; color: var(--ink3); margin-bottom: .3rem; }
.panel p { color: var(--ink2); font-size: .95rem; }
.panel .big { font: 800 2.2rem/1 var(--f-display); }

.tracks { display: grid; grid-template-columns: repeat(auto-fit, minmax(300px, 1fr)); gap: 1.2rem; }
.track { display: flex; flex-direction: column; gap: .5rem; text-decoration: none; color: var(--ink); background: var(--card); border: 1.5px solid var(--ink); border-radius: var(--r); padding: 1.2rem 1.3rem; box-shadow: var(--shadow); transition: transform .12s, box-shadow .12s; position: relative; overflow: hidden; }
.track::before { content: ""; position: absolute; left: 0; top: 0; bottom: 0; width: 6px; background: var(--tc, var(--ink)); }
.track:hover { transform: translate(-2px, -2px); box-shadow: 5px 5px 0 var(--rule2); color: var(--ink); }
.track .tk { font: 700 .72rem var(--f-body); letter-spacing: .14em; text-transform: uppercase; color: var(--tc, var(--ink3)); }
.track h3 { font-size: 1.5rem; }
.track p { margin: 0; color: var(--ink2); font-size: .95rem; }
.track .meta { margin-top: auto; display: flex; gap: .6rem; align-items: center; font-size: .82rem; color: var(--ink3); }
.progress { flex: 1; height: 7px; border-radius: 4px; background: var(--rule); overflow: hidden; }
.progress > i { display: block; height: 100%; background: var(--tc, var(--ink)); border-radius: 4px; transition: width .4s; }

.principles { display: grid; grid-template-columns: repeat(auto-fit, minmax(230px, 1fr)); gap: 1rem; counter-reset: pr; }
.principle { position: relative; padding: 1rem 1.1rem 1rem 3.2rem; border-top: 2px solid var(--ink); }
.principle::before { counter-increment: pr; content: counter(pr); position: absolute; left: 0; top: .8rem; font: 800 2rem/1 var(--f-display); color: var(--trap); width: 2.6rem; text-align: center; }
.principle b { display: block; font-family: var(--f-display); font-size: 1.1rem; }
.principle span { font-size: .92rem; color: var(--ink2); }

/* ------------------------------------------------------------------ module & lesson pages */
.page-head { padding: clamp(1.6rem, 4vw, 3rem) 0 1rem; }
.crumbs { font-size: .85rem; color: var(--ink3); margin-bottom: .6rem; }
.crumbs a { color: var(--ink3); }
.page-head h1 { font-size: clamp(2rem, 5vw, 3.4rem); max-width: 22ch; }
.page-head .lede { font-size: 1.15rem; color: var(--ink2); max-width: 44rem; margin-top: .7rem; }

.lessons { display: grid; gap: .8rem; margin-top: 1rem; }
.lrow { display: grid; grid-template-columns: 3rem 1fr auto; gap: 1rem; align-items: center; background: var(--card); border: 1.5px solid var(--ink); border-radius: var(--r); padding: .9rem 1.1rem; text-decoration: none; color: var(--ink); box-shadow: 2px 2px 0 var(--rule2); }
.lrow:hover { transform: translate(-1px, -1px); box-shadow: 4px 4px 0 var(--rule2); color: var(--ink); }
.lrow .n { font: 800 1.7rem var(--f-display); color: var(--tc, var(--ink3)); text-align: center; }
.lrow.done .n::after { content: "✓"; display: block; font: 700 .8rem var(--f-body); color: var(--ok); }
.lrow h3 { font-size: 1.2rem; margin-bottom: .15rem; }
.lrow p { margin: 0; font-size: .9rem; color: var(--ink3); }
.lrow .min { font: 600 .8rem var(--f-mono); color: var(--ink3); white-space: nowrap; }

.lesson { display: grid; grid-template-columns: 210px minmax(0, 1fr); gap: clamp(1.5rem, 4vw, 3.5rem); align-items: start; }
.outline { position: sticky; top: 4.6rem; font-size: .88rem; padding-top: 1rem; }
.outline h4 { font: 700 .72rem var(--f-body); letter-spacing: .14em; text-transform: uppercase; color: var(--ink3); margin-bottom: .6rem; }
.outline a { display: block; color: var(--ink2); text-decoration: none; padding: .3rem 0 .3rem .8rem; border-left: 2px solid var(--rule); line-height: 1.35; }
.outline a:hover { color: var(--ink); border-color: var(--ink); }
.outline a.on { color: var(--ink); font-weight: 700; border-color: var(--trap); }
.lbody { min-width: 0; max-width: 46rem; padding-bottom: 2rem; }
.lbody h2 { font-size: clamp(1.55rem, 3vw, 2rem); margin: 2.8rem 0 .9rem; padding-top: .4rem; border-top: 1.5px solid var(--ink); scroll-margin-top: 5rem; }
.lbody h2:first-child { margin-top: 0; }
.lbody > p, .lbody .lst { font-size: 1.07rem; }
.lbody .lab, .lbody .boss { margin-left: calc(-1 * clamp(0px, 3vw, 2rem)); margin-right: calc(-1 * clamp(0px, 3vw, 2rem)); }
.lesson-head { padding: clamp(1.4rem, 3vw, 2.4rem) 0 1.4rem; max-width: 52rem; }
.kicker { font: 700 .78rem var(--f-body); letter-spacing: .14em; text-transform: uppercase; color: var(--tc, var(--trap)); margin-bottom: .5rem; }
.lesson-head h1 { font-size: clamp(2.1rem, 5vw, 3.5rem); }
.lesson-meta { display: flex; gap: .5rem 1rem; flex-wrap: wrap; align-items: center; margin-top: .9rem; font-size: .88rem; color: var(--ink3); }
.objectives { margin-top: 1.2rem; padding: 1rem 1.2rem; background: var(--card); border: 1px solid var(--rule2); border-radius: var(--r); }
.objectives h4 { font: 700 .72rem var(--f-body); letter-spacing: .14em; text-transform: uppercase; color: var(--ink3); margin-bottom: .4rem; }
.lst { margin: 0 0 1.1em; padding-left: 1.3rem; }
.lst li { margin-bottom: .4em; }
.lst li::marker { color: var(--trap); font-weight: 700; }
.lesson-end { margin-top: 3rem; padding: 1.4rem; border: 2px dashed var(--rule2); border-radius: var(--r); display: flex; gap: 1rem; flex-wrap: wrap; align-items: center; justify-content: space-between; }
.lesson-end b { font: 700 1.2rem var(--f-display); }

/* ------------------------------------------------------------------ blocks */
.block { margin: 1.6rem 0; padding: 1.1rem 1.2rem 1.2rem; background: var(--card); border: 1.5px solid var(--ink); border-radius: var(--r); box-shadow: var(--shadow); }
.blk-tag { display: flex; align-items: center; gap: .6rem; font: 800 .72rem var(--f-body); letter-spacing: .14em; text-transform: uppercase; color: var(--ink); margin-bottom: .7rem; }
.blk-tag > span:first-child { background: var(--ink); color: var(--paper); padding: .15rem .5rem; border-radius: 3px; }
.badge { font: 700 .7rem var(--f-body); color: var(--ink3); letter-spacing: .06em; }
.badge.ok { color: var(--ok); }
.badge.ok::before { content: "✓ "; }

.callout { display: grid; grid-template-columns: auto 1fr; gap: 0 1rem; margin: 1.4rem 0; padding: .9rem 1.1rem; border-radius: var(--r); border: 1.5px solid; background: var(--card); }
.callout-k { font: 800 .7rem var(--f-body); letter-spacing: .12em; text-transform: uppercase; padding-top: .25rem; min-width: 5.2rem; }
.callout-t { display: block; margin-bottom: .2rem; }
.callout-b { min-width: 0; } .callout-b > :last-child { margin-bottom: 0; }
.callout.trap { border-color: var(--trap); background: var(--trapbg); } .callout.trap .callout-k { color: var(--trap); }
.callout.insight { border-color: var(--ins); background: var(--insbg); } .callout.insight .callout-k { color: var(--ins); }
.callout.rule { border-color: var(--warn); background: var(--warnbg); } .callout.rule .callout-k { color: var(--warn); }
.callout.say { border-color: var(--blue); background: color-mix(in srgb, var(--blue) 8%, var(--card)); } .callout.say .callout-k { color: var(--blue); }
.callout.note, .callout.why { border-color: var(--rule2); } .callout.note .callout-k, .callout.why .callout-k { color: var(--ink3); }
@media (max-width: 560px) { .callout { grid-template-columns: 1fr; } }

.stepper { list-style: none; margin: 0; padding: 0; counter-reset: st; }
.step { display: grid; grid-template-columns: 2rem 1fr; gap: .8rem; padding: .7rem 0; border-top: 1px dashed var(--rule2); animation: pop .35s ease both; }
.step:first-child { border-top: 0; }
.step.hidden { display: none; }
.step-n { width: 1.8rem; height: 1.8rem; border-radius: 50%; background: var(--ink); color: var(--paper); font: 700 .85rem/1.8rem var(--f-mono); text-align: center; }
.step-b > div > :last-child { margin-bottom: 0; }
.step-h { display: block; font-family: var(--f-display); font-size: 1.08rem; margin-bottom: .15rem; }
.stepper-title { font: 700 1.2rem var(--f-display); margin-bottom: .4rem; }
.stepper-ctl { display: flex; gap: .6rem; margin-top: .8rem; }
@keyframes pop { from { opacity: 0; transform: translateY(6px); } to { opacity: 1; transform: none; } }

.predict { border-color: var(--blue); }
.predict .blk-tag > span:first-child { background: var(--blue); color: #fff; }
.predict-q { font: 500 1.12rem/1.45 var(--f-display); margin-bottom: .8rem; }
.predict-ctl { display: grid; grid-template-columns: 1fr auto; gap: 1rem; align-items: end; }
@media (max-width: 560px) { .predict-ctl { grid-template-columns: 1fr; } }
.ptrack { position: relative; height: 12px; margin: 1.2rem 0 .4rem; background: var(--rule); border-radius: 6px; }
.pm { position: absolute; top: -5px; width: 4px; height: 22px; border-radius: 2px; transform: translateX(-2px); }
.pm.guess { background: var(--ink); } .pm.truth { background: var(--ins); width: 6px; }
.predict-res { margin: .8rem 0 .4rem; padding: .5rem .8rem; border-radius: 4px; }
.predict-res.ok { background: var(--okbg); color: var(--ok); } .predict-res.miss { background: var(--warnbg); color: var(--warn); }
.predict-why { color: var(--ink2); }
.predict-why > :last-child { margin-bottom: 0; }

.check .check-q { font-size: 1.06rem; margin-bottom: .8rem; }
.fb { margin: .8rem 0 0; }
.fb:not(:empty) { padding: .6rem .9rem; border-radius: 4px; border-left: 4px solid; }
.fb.ok { background: var(--okbg); border-color: var(--ok); } .fb.bad { background: var(--trapbg); border-color: var(--trap); } .fb.warn { background: var(--warnbg); border-color: var(--warn); }
.fb > :last-child { margin-bottom: 0; }
.hints { margin: .6rem 0 0; padding-left: 1.4rem; color: var(--ink2); font-size: .95rem; flex-basis: 100%; }
.hints li { margin: .3rem 0; }
.hint-wrap { display: contents; }
.disc { margin-top: .9rem; border: 1px solid var(--rule2); border-radius: var(--r); background: var(--paper2); }
.disc summary { cursor: pointer; padding: .6rem .9rem; font-weight: 700; font-size: .92rem; }
.disc-b { padding: .2rem 1rem 1rem; } .disc-b > :last-child { margin-bottom: 0; }
.grade { display: flex; gap: .5rem; align-items: center; flex-wrap: wrap; margin-top: .8rem; font-weight: 600; }
.mc { display: grid; gap: .5rem; margin: .5rem 0; }
.mc-o { text-align: left; font: 500 1rem/1.4 var(--f-body); padding: .65rem .9rem; border: 1.5px solid var(--rule2); background: var(--card); color: var(--ink); border-radius: 5px; cursor: pointer; }
.mc-o:hover:not(:disabled) { border-color: var(--ink); background: var(--paper2); }
.mc-o.right { border-color: var(--ok); background: var(--okbg); }
.mc-o.wrong { border-color: var(--trap); background: var(--trapbg); }
.mc-o:disabled { cursor: default; color: var(--ink); }

.costumes .costume, .followups .costume { border-top: 1px dashed var(--rule2); }
.costume summary { cursor: pointer; padding: .7rem 0; font-weight: 600; }
.costume-a { padding: 0 0 .9rem 1rem; border-left: 3px solid var(--ins); margin-left: .2rem; color: var(--ink2); }
.costume-a > :last-child { margin-bottom: 0; }

.tbl-wrap { overflow-x: auto; margin: 1.2rem 0; }
.tbl { border-collapse: collapse; width: 100%; font-size: .95rem; background: var(--card); }
.tbl caption { text-align: left; font-weight: 700; padding: 0 0 .4rem; font-family: var(--f-display); font-size: 1.05rem; }
.tbl th, .tbl td { border: 1px solid var(--rule2); padding: .45rem .7rem; text-align: left; vertical-align: top; }
.tbl th { background: var(--ink); color: var(--paper); font-weight: 600; }
.tbl td:first-child { font-weight: 600; }

.recap { margin: 2rem 0; padding: 1.1rem 1.3rem; border: 2px solid var(--ink); border-radius: var(--r); background: repeating-linear-gradient(135deg, transparent 0 12px, var(--grid) 12px 13px), var(--card); }
.recap-k { font: 800 .75rem var(--f-body); letter-spacing: .16em; text-transform: uppercase; color: var(--trap); margin-bottom: .5rem; }
.recap .lst { margin-bottom: 0; }

/* ------------------------------------------------------------------ labs */
.lab { position: relative; margin: 2.2rem 0; padding: 1.5rem 1.3rem 1.3rem; border: 1.5px solid var(--ink); border-radius: var(--r); background: var(--card);
  background-image: linear-gradient(var(--grid) 1px, transparent 1px), linear-gradient(90deg, var(--grid) 1px, transparent 1px); background-size: 16px 16px; box-shadow: var(--shadow-lg); }
.lab-tab { position: absolute; top: -.8rem; left: 1rem; background: var(--ink); color: var(--paper); font: 800 .72rem var(--f-body); letter-spacing: .16em; text-transform: uppercase; padding: .25rem .7rem; border-radius: 3px; }
.lab-title { font-size: 1.35rem; margin: .1rem 0 .3rem; }
.lab-intro { color: var(--ink2); font-size: .98rem; margin-bottom: .8rem; }
.lab-body { min-width: 0; }
.lab-note { font-size: .88rem; color: var(--ink3); margin: .6rem 0 0; }
.lab-cols { display: grid; grid-template-columns: repeat(auto-fit, minmax(300px, 1fr)); gap: 1.2rem; align-items: start; }
.lab canvas { max-width: 100%; height: auto; border: 1px solid var(--rule2); border-radius: var(--r); background: var(--card); touch-action: none; }
.readout { font: 600 .95rem var(--f-mono); background: var(--paper2); border-radius: var(--r); padding: .6rem .8rem; border: 1px solid var(--rule); }
.readout b { color: var(--ink); }
.verdict { margin: .7rem 0 0; padding: .6rem .9rem; border-radius: 4px; border-left: 4px solid var(--ins); background: var(--insbg); font-size: .95rem; }
.verdict.bad { border-color: var(--trap); background: var(--trapbg); }
.verdict.warn { border-color: var(--warn); background: var(--warnbg); }
.verdict > :last-child { margin-bottom: 0; }
.lab .tbl { font-size: .88rem; } .lab .tbl td, .lab .tbl th { padding: .3rem .5rem; }
.num { font-family: var(--f-mono); text-align: right !important; font-variant-numeric: tabular-nums; }
.neg { color: var(--trap); font-weight: 700; } .pos { color: var(--ok); }
.heat td { text-align: center !important; font-family: var(--f-mono); font-size: .82rem; }

/* ------------------------------------------------------------------ boss problem */
.boss { margin: 2.6rem 0; padding: 1.3rem; border: 2px solid var(--ink); border-radius: var(--r); background: var(--paper2); box-shadow: var(--shadow-lg); position: relative; }
.boss-head { display: flex; align-items: center; gap: .8rem; margin-bottom: 1rem; flex-wrap: wrap; }
.boss-k { background: var(--trap); color: #fff; font: 800 .74rem var(--f-body); letter-spacing: .16em; text-transform: uppercase; padding: .25rem .7rem; border-radius: 3px; }
.lvl { font: 700 .75rem var(--f-mono); color: var(--ink3); }
.boss .qcard { margin-bottom: 1rem; }
.boss .qcard-q { font-size: 1.28rem; }
.boss-tools { display: flex; align-items: center; gap: .8rem; margin-bottom: .6rem; }
.clock { font: 700 1.1rem var(--f-mono); } .clock.over { color: var(--trap); }
.boss-note { font-size: .95rem; color: var(--ink2); }
.boss-after { margin-top: 1.2rem; padding-top: 1rem; border-top: 2px dashed var(--rule2); }
.rubric { margin-top: 1.2rem; padding: 1rem; background: var(--card); border: 1.5px solid var(--ink); border-radius: var(--r); }
.rb { display: flex; gap: .6rem; align-items: flex-start; padding: .35rem 0; cursor: pointer; }
.rb input { margin-top: .35rem; width: 1.1rem; height: 1.1rem; accent-color: var(--ink); }
.rubric-res { font-weight: 700; }
.followups { margin-top: 1.2rem; }

/* ------------------------------------------------------------------ practice / review / drills / progress */
.modes { display: grid; grid-template-columns: repeat(auto-fit, minmax(250px, 1fr)); gap: 1rem; margin: 1rem 0 2rem; }
.mode { display: flex; flex-direction: column; gap: .4rem; text-align: left; font: inherit; color: var(--ink); background: var(--card); border: 1.5px solid var(--ink); border-radius: var(--r); padding: 1.1rem 1.2rem; cursor: pointer; box-shadow: var(--shadow); text-decoration: none; }
.mode:hover { transform: translate(-2px, -2px); box-shadow: 5px 5px 0 var(--rule2); color: var(--ink); }
.mode b { font: 700 1.2rem var(--f-display); } .mode span { font-size: .92rem; color: var(--ink2); }
.mode .k { font: 800 .7rem var(--f-body); letter-spacing: .14em; text-transform: uppercase; color: var(--trap); }
.gens { display: grid; grid-template-columns: repeat(auto-fill, minmax(260px, 1fr)); gap: .7rem; }
.gen { display: flex; justify-content: space-between; gap: .6rem; align-items: center; text-align: left; font: inherit; background: var(--card); color: var(--ink); border: 1px solid var(--rule2); border-radius: var(--r); padding: .6rem .8rem; cursor: pointer; }
.gen:hover { border-color: var(--ink); }
.gen b { font-weight: 600; font-size: .95rem; display: block; }
.gen small { color: var(--ink3); }
.gen .acc { font: 700 .8rem var(--f-mono); color: var(--ink3); white-space: nowrap; }
.session { max-width: 46rem; margin: 1.5rem auto 0; }
.session-top { display: flex; justify-content: space-between; align-items: center; gap: 1rem; margin-bottom: 1rem; flex-wrap: wrap; }
.q-prompt { font: 500 1.28rem/1.45 var(--f-display); margin: .6rem 0 1.2rem; }
.explain { margin-top: 1rem; padding: .9rem 1.1rem; background: var(--paper2); border-left: 4px solid var(--ins); border-radius: 4px; }
.explain > :last-child { margin-bottom: 0; }
.flash { perspective: 1200px; max-width: 40rem; margin: 1.2rem auto; }
.flash-card { min-height: 15rem; padding: 2rem 1.6rem; background: var(--card); border: 2px solid var(--ink); border-radius: var(--r); box-shadow: var(--shadow-lg); display: flex; flex-direction: column; justify-content: center; gap: .8rem; cursor: pointer; }
.flash-card .side { font: 800 .7rem var(--f-body); letter-spacing: .16em; text-transform: uppercase; color: var(--trap); }
.flash-card .face { font: 500 1.3rem/1.45 var(--f-display); }
.flash-card .face > :last-child { margin-bottom: 0; }
.rate { display: flex; gap: .6rem; justify-content: center; flex-wrap: wrap; margin-top: 1rem; }
.meter { display: flex; gap: 4px; }
.meter i { width: 10px; height: 10px; border-radius: 2px; background: var(--rule2); } .meter i.on { background: var(--ok); }
.drill-q { font: 700 clamp(2.2rem, 7vw, 3.6rem) var(--f-mono); text-align: center; margin: 1.4rem 0 1rem; letter-spacing: .02em; }
.drill-in { display: flex; gap: .6rem; justify-content: center; }
.drill-in .ans { width: 12rem; font-size: 1.4rem; text-align: center; }
.timebar { height: 8px; background: var(--rule); border-radius: 4px; overflow: hidden; margin: .6rem 0 1rem; }
.timebar i { display: block; height: 100%; background: var(--ink); width: 100%; transition: width 1s linear; }

.heatmap { display: grid; grid-template-columns: repeat(auto-fill, minmax(190px, 1fr)); gap: .6rem; }
.tile { padding: .7rem .8rem; border: 1.5px solid var(--ink); border-radius: var(--r); background: var(--card); position: relative; overflow: hidden; }
.tile::before { content: ""; position: absolute; left: 0; bottom: 0; height: 5px; width: var(--m, 0%); background: var(--c, var(--ink3)); }
.tile b { display: block; font-size: .92rem; line-height: 1.3; }
.tile small { color: var(--ink3); font-family: var(--f-mono); }
.tile.none { border-style: dashed; border-color: var(--rule2); background: transparent; }
.toolbox-grid { display: grid; grid-template-columns: repeat(auto-fit, minmax(300px, 1fr)); gap: 1rem; }
.formula { padding: .8rem 1rem; background: var(--card); border: 1px solid var(--rule2); border-radius: var(--r); }
.formula b { font-size: .88rem; color: var(--ink3); display: block; margin-bottom: .2rem; font-weight: 600; }
.formula .eq { margin: .3rem 0; padding: .3rem .5rem; border-left-width: 3px; }
.formula .eq math { font-size: 1.15em; }
.formula p { margin: .3rem 0 0; font-size: .86rem; color: var(--ink2); }
.search { width: 100%; max-width: 26rem; font: 1rem var(--f-body); padding: .65rem .9rem; border: 1.5px solid var(--ink); border-radius: 5px; background: var(--card); color: var(--ink); }

.toast { position: fixed; left: 50%; bottom: 1.5rem; transform: translateX(-50%); background: var(--ink); color: var(--paper); padding: .6rem 1.1rem; border-radius: 6px; font-weight: 600; z-index: 200; box-shadow: var(--shadow-lg); transition: opacity .4s; }
.toast.out { opacity: 0; }

/* ------------------------------------------------------------------ responsive */
@media (max-width: 1020px) {
  .lesson { grid-template-columns: minmax(0, 1fr); }
  .outline { display: none; }
  .lbody .lab, .lbody .boss { margin-left: 0; margin-right: 0; }
}
@media (max-width: 640px) {
  body { font-size: 1rem; }
  .nav a { padding: .3rem .5rem; font-size: .85rem; }
  .lrow { grid-template-columns: 2.2rem 1fr; } .lrow .min { display: none; }
  .qcards .qcard { transform: none !important; }
  .qcard { padding-left: 2.6rem; } .qcard::before { left: 1.8rem; } .qcard-tag { left: 2.6rem; }
  .block, .lab, .boss { padding-left: .9rem; padding-right: .9rem; }
}

/* ------------------------------------------------------------------ three-statement flow diagram */
.flow3 { display: grid; grid-template-columns: 1fr auto 1fr auto 1fr; gap: .6rem; align-items: center; margin: 1.4rem 0; }
.f3 { background: var(--card); border: 1.5px solid var(--ink); border-radius: var(--r); padding: .8rem .9rem; box-shadow: var(--shadow); font-size: .9rem; line-height: 1.5; }
.f3 b { display: block; font: 700 1.05rem var(--f-display); margin-bottom: .3rem; }
.f3 span { color: var(--ink2); } .f3 i { font-style: normal; font-weight: 700; color: var(--trap); }
.f3-arr { font-size: .74rem; color: var(--ink3); text-align: center; max-width: 9rem; line-height: 1.3; }
@media (max-width: 760px) { .flow3 { grid-template-columns: 1fr; } .f3-arr { max-width: none; } }

@media (max-width: 640px) { .top { position: static; } }