/* AP Chemistry I — Final study site (Ch 13–15) */

:root {
  --bg: #f5f6fa;
  --surface: #ffffff;
  --surface-2: #eef1f8;
  --text: #172033;
  --muted: #5a657c;
  --line: #dce1ed;
  --primary: #1b4fb3;
  --primary-ink: #ffffff;
  --primary-weak: #e5edfc;
  --green: #0c8f63;
  --green-weak: #def4ea;
  --amber: #a85a00;
  --amber-weak: #fff1d9;
  --red: #c0262d;
  --red-weak: #fde8e8;
  --c13: #2458c7;
  --c14: #0c8f63;
  --c15: #c4620a;
  --shadow: 0 1px 2px rgba(20, 30, 60, .06), 0 4px 14px rgba(20, 30, 60, .05);
  --radius: 12px;
  --font: "Pretendard Variable", Pretendard, -apple-system, BlinkMacSystemFont, "Segoe UI", "Malgun Gothic", "Apple SD Gothic Neo", "Noto Sans KR", system-ui, sans-serif;
  --mono: ui-monospace, SFMono-Regular, Consolas, "Courier New", monospace;
  color-scheme: light;
}

@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    --bg: #0e1320;
    --surface: #171e2f;
    --surface-2: #1f283c;
    --text: #e7ebf6;
    --muted: #98a4be;
    --line: #2b3550;
    --primary: #79a6ff;
    --primary-ink: #0b1226;
    --primary-weak: #1b2a4d;
    --green: #4fd1a1;
    --green-weak: #143428;
    --amber: #f3b25c;
    --amber-weak: #3a2c12;
    --red: #ff8a8f;
    --red-weak: #3b1a1d;
    --c13: #7aa5ff;
    --c14: #4fd1a1;
    --c15: #f0a45e;
    --shadow: 0 1px 2px rgba(0, 0, 0, .4), 0 6px 18px rgba(0, 0, 0, .3);
    color-scheme: dark;
  }
}

:root[data-theme="dark"] {
  --bg: #0e1320;
  --surface: #171e2f;
  --surface-2: #1f283c;
  --text: #e7ebf6;
  --muted: #98a4be;
  --line: #2b3550;
  --primary: #79a6ff;
  --primary-ink: #0b1226;
  --primary-weak: #1b2a4d;
  --green: #4fd1a1;
  --green-weak: #143428;
  --amber: #f3b25c;
  --amber-weak: #3a2c12;
  --red: #ff8a8f;
  --red-weak: #3b1a1d;
  --c13: #7aa5ff;
  --c14: #4fd1a1;
  --c15: #f0a45e;
  --shadow: 0 1px 2px rgba(0, 0, 0, .4), 0 6px 18px rgba(0, 0, 0, .3);
  color-scheme: dark;
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; scroll-padding-top: 132px; -webkit-text-size-adjust: 100%; }
body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font-family: var(--font);
  font-size: 16px;
  line-height: 1.7;
  word-break: keep-all;
  overflow-wrap: break-word;
}
@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  * { transition: none !important; animation: none !important; }
}

a { color: var(--primary); }
button { font: inherit; color: inherit; cursor: pointer; }
:focus-visible { outline: 3px solid var(--primary); outline-offset: 2px; border-radius: 6px; }
.sr-only { position: absolute; width: 1px; height: 1px; overflow: hidden; clip: rect(0 0 0 0); white-space: nowrap; }
.hide { display: none !important; }
.muted { color: var(--muted); }
.nowrap { white-space: nowrap; }

/* ---------- header / tabs ---------- */
.site-header {
  position: sticky; top: 0; z-index: 30;
  background: color-mix(in srgb, var(--surface) 92%, transparent);
  backdrop-filter: saturate(1.4) blur(10px);
  border-bottom: 1px solid var(--line);
}
.header-inner {
  max-width: 1120px; margin: 0 auto; padding: 10px 16px 0;
  display: flex; align-items: center; justify-content: space-between; gap: 12px;
}
.brand { display: flex; align-items: baseline; gap: 10px; min-width: 0; }
.brand b { font-size: 1.05rem; letter-spacing: -.01em; white-space: nowrap; }
.brand span { font-size: .82rem; color: var(--muted); white-space: nowrap; overflow: hidden; text-overflow: ellipsis; }
.theme-btn {
  border: 1px solid var(--line); background: var(--surface); border-radius: 999px;
  width: 38px; height: 38px; display: grid; place-items: center; flex: none;
}
.theme-btn:hover { background: var(--surface-2); }
.tabs {
  max-width: 1120px; margin: 0 auto; padding: 6px 12px 0;
  display: flex; gap: 4px;
}
.tab {
  flex: 1 1 0; min-width: 0;
  border: 0; background: transparent; padding: 10px 8px 12px;
  font-weight: 600; font-size: .98rem; color: var(--muted);
  border-bottom: 3px solid transparent; display: flex; gap: 8px; align-items: center; justify-content: center;
  transition: color .15s, border-color .15s, background .15s; border-radius: 10px 10px 0 0;
}
.tab svg { width: 18px; height: 18px; flex: none; }
.tab:hover { color: var(--text); background: var(--surface-2); }
.tab[aria-selected="true"] { color: var(--primary); border-bottom-color: var(--primary); }
@media (max-width: 520px) {
  .brand span { display: none; }
  .tab { font-size: .9rem; gap: 6px; padding-inline: 4px; }
}

main { max-width: 1120px; margin: 0 auto; padding: 20px 16px 80px; }
.tab-panel[hidden] { display: none; }

/* ---------- generic building blocks ---------- */
.card {
  background: var(--surface); border: 1px solid var(--line); border-radius: var(--radius);
  box-shadow: var(--shadow); padding: 18px 20px;
}
.btn {
  border: 1px solid var(--line); background: var(--surface); border-radius: 10px;
  padding: 8px 14px; font-weight: 600; font-size: .92rem; line-height: 1.3;
  transition: background .15s, border-color .15s, transform .05s;
}
.btn:hover { background: var(--surface-2); }
.btn:active { transform: translateY(1px); }
.btn-primary { background: var(--primary); border-color: var(--primary); color: var(--primary-ink); }
.btn-primary:hover { background: color-mix(in srgb, var(--primary) 88%, #000); }
.btn-ok { background: var(--green-weak); border-color: color-mix(in srgb, var(--green) 45%, transparent); color: var(--green); }
.btn-bad { background: var(--red-weak); border-color: color-mix(in srgb, var(--red) 45%, transparent); color: var(--red); }
.btn[disabled] { opacity: .5; cursor: not-allowed; }
.chip {
  border: 1px solid var(--line); background: var(--surface); border-radius: 999px;
  padding: 5px 13px; font-size: .88rem; font-weight: 600; color: var(--muted);
  transition: all .15s;
}
.chip:hover { color: var(--text); background: var(--surface-2); }
.chip[aria-pressed="true"] { background: var(--primary); border-color: var(--primary); color: var(--primary-ink); }
.chip.c13[aria-pressed="true"] { background: var(--c13); border-color: var(--c13); }
.chip.c14[aria-pressed="true"] { background: var(--c14); border-color: var(--c14); }
.chip.c15[aria-pressed="true"] { background: var(--c15); border-color: var(--c15); }

.badge {
  display: inline-flex; align-items: center; gap: 4px;
  font-size: .74rem; font-weight: 700; padding: 2px 9px; border-radius: 999px;
  background: var(--surface-2); color: var(--muted); border: 1px solid var(--line); letter-spacing: .01em;
}
.badge.hw { background: var(--red-weak); color: var(--red); border-color: transparent; }
.badge.ap { background: var(--primary-weak); color: var(--primary); border-color: transparent; }
.badge.book { background: var(--green-weak); color: var(--green); border-color: transparent; }
.badge.gen { background: var(--amber-weak); color: var(--amber); border-color: transparent; }
.badge.ch13 { color: var(--c13); } .badge.ch14 { color: var(--c14); } .badge.ch15 { color: var(--c15); }

/* ---------- STUDY ---------- */
.study-layout { display: grid; grid-template-columns: 236px minmax(0, 1fr); gap: 28px; align-items: start; }
.toc {
  position: sticky; top: 128px; max-height: calc(100vh - 150px); overflow: auto;
  padding: 14px 8px 14px 0; font-size: .9rem;
}
.toc h4 { margin: 14px 0 4px 10px; font-size: .74rem; letter-spacing: .08em; text-transform: uppercase; color: var(--muted); }
.toc h4:first-child { margin-top: 0; }
.toc a {
  display: block; padding: 5px 10px; border-radius: 8px; color: var(--text); text-decoration: none; line-height: 1.4;
  border-left: 3px solid transparent;
}
.toc a:hover { background: var(--surface-2); }
.toc a.active { background: var(--primary-weak); color: var(--primary); font-weight: 700; border-left-color: var(--primary); }
.toc a.sub { padding-left: 22px; font-size: .84rem; color: var(--muted); }
.toc a.out { text-decoration: line-through; text-decoration-color: color-mix(in srgb, var(--red) 60%, transparent); opacity: .7; }
@media (max-width: 960px) {
  .study-layout { grid-template-columns: minmax(0, 1fr); gap: 0; }
  .toc {
    position: sticky; top: 98px; z-index: 20; max-height: none; overflow-x: auto; overflow-y: hidden;
    display: flex; gap: 6px; padding: 8px 2px; margin: -8px -16px 10px; padding-inline: 16px;
    background: color-mix(in srgb, var(--bg) 94%, transparent); backdrop-filter: blur(8px);
    border-bottom: 1px solid var(--line); scrollbar-width: none;
  }
  .toc::-webkit-scrollbar { display: none; }
  .toc h4 { display: none; }
  .toc a { white-space: nowrap; border: 1px solid var(--line); border-radius: 999px; background: var(--surface); padding: 4px 12px; font-size: .84rem; }
  .toc a.sub { display: none; }
  .toc a.active { border-left-width: 1px; }
  html { scroll-padding-top: 150px; }
}

.hero { padding: 6px 0 18px; }
.hero h1 { font-size: clamp(1.5rem, 4vw, 2.1rem); line-height: 1.25; letter-spacing: -.02em; margin: 0 0 6px; }
.hero p { margin: 0; color: var(--muted); }
.scope-grid { display: grid; grid-template-columns: repeat(3, 1fr); gap: 14px; margin: 16px 0 6px; }
@media (max-width: 780px) { .scope-grid { grid-template-columns: 1fr; } }
.scope-card { border-top: 4px solid var(--accent, var(--primary)); padding: 14px 16px 12px; }
.scope-card.c13 { --accent: var(--c13); } .scope-card.c14 { --accent: var(--c14); } .scope-card.c15 { --accent: var(--c15); }
.scope-card h3 { margin: 0 0 6px; font-size: 1.02rem; }
.scope-card h3 span { color: var(--accent); }
.scope-card ul { margin: 0; padding-left: 1.1em; font-size: .9rem; }
.scope-card li { margin: 2px 0; }
.scope-card li.x { color: var(--muted); text-decoration: line-through; text-decoration-color: color-mix(in srgb, var(--red) 70%, transparent); }
.legend { font-size: .86rem; color: var(--muted); margin: 8px 0 0; }

.chapter { margin-top: 44px; }
.chapter:first-of-type { margin-top: 20px; }
.chapter-head {
  display: flex; align-items: center; gap: 14px; margin: 0 0 14px; padding: 14px 18px;
  border-radius: var(--radius); background: var(--surface); border: 1px solid var(--line);
  border-left: 8px solid var(--accent); box-shadow: var(--shadow);
}
.chapter.c13 { --accent: var(--c13); } .chapter.c14 { --accent: var(--c14); } .chapter.c15 { --accent: var(--c15); }
.chapter-head .num { font-size: 2rem; font-weight: 800; color: var(--accent); line-height: 1; letter-spacing: -.03em; }
.chapter-head h2 { margin: 0; font-size: 1.35rem; line-height: 1.25; letter-spacing: -.01em; }
.chapter-head p { margin: 2px 0 0; font-size: .9rem; color: var(--muted); }

.sec { margin: 28px 0 0; }
.sec > h3 {
  font-size: 1.2rem; margin: 0 0 10px; padding-bottom: 6px; border-bottom: 2px solid var(--line);
  letter-spacing: -.01em; line-height: 1.45;
}
.sec > h3 .sn { color: var(--accent); font-weight: 800; font-size: .95em; margin-right: .5em; }
.sec h4 { margin: 22px 0 6px; font-size: 1.02rem; }
.sec > h3.out-title { color: var(--muted); }
.sec > h3.out-title .strike { text-decoration: line-through; text-decoration-color: color-mix(in srgb, var(--red) 60%, transparent); }
.sec > h3.out-title .badge { vertical-align: 2px; margin-left: 6px; }
details.excl-sec { opacity: .92; }
.sec p { margin: 8px 0; }
.sec ul, .sec ol { margin: 8px 0; padding-left: 1.3em; }
.sec li { margin: 3px 0; }

.eq {
  background: var(--surface); border: 1px solid var(--line); border-left: 5px solid var(--accent, var(--primary));
  border-radius: 10px; padding: 10px 16px; margin: 12px 0; overflow-x: auto; text-align: center;
}
.eq .cap { display: block; text-align: left; font-size: .8rem; font-weight: 700; color: var(--accent, var(--primary)); margin-bottom: 2px; letter-spacing: .02em; }
.callout {
  border-radius: 10px; padding: 11px 16px; margin: 14px 0; border: 1px solid transparent;
  background: var(--primary-weak);
}
.callout > b:first-child, .callout .ttl { display: block; font-size: .8rem; letter-spacing: .05em; margin-bottom: 2px; font-weight: 800; }
.callout.def { background: var(--primary-weak); border-color: color-mix(in srgb, var(--primary) 25%, transparent); }
.callout.def .ttl { color: var(--primary); }
.callout.tip { background: var(--green-weak); border-color: color-mix(in srgb, var(--green) 25%, transparent); }
.callout.tip .ttl { color: var(--green); }
.callout.warn { background: var(--amber-weak); border-color: color-mix(in srgb, var(--amber) 30%, transparent); }
.callout.warn .ttl { color: var(--amber); }
.callout.excl {
  background: repeating-linear-gradient(135deg, var(--surface-2), var(--surface-2) 10px, color-mix(in srgb, var(--surface-2) 70%, var(--line)) 10px, color-mix(in srgb, var(--surface-2) 70%, var(--line)) 20px);
  border: 1px dashed var(--muted); color: var(--muted);
}
.callout.excl .ttl { color: var(--red); }
.callout p:first-of-type { margin-top: 0; } .callout p:last-child { margin-bottom: 0; }
.callout ul { margin: 4px 0; }

.tbl-wrap { overflow-x: auto; margin: 12px 0; border: 1px solid var(--line); border-radius: 10px; background: var(--surface); }
table.tbl { border-collapse: collapse; width: 100%; font-size: .93rem; font-variant-numeric: tabular-nums; }
.tbl th, .tbl td { padding: 8px 12px; text-align: center; border-bottom: 1px solid var(--line); vertical-align: middle; }
.tbl th { background: var(--surface-2); font-size: .82rem; letter-spacing: .02em; font-weight: 700; white-space: nowrap; }
.tbl tr:last-child td { border-bottom: 0; }
.tbl td.l, .tbl th.l { text-align: left; }
.tbl td .katex { display: inline-block; max-width: 100%; }
.tbl tbody tr:hover td { background: color-mix(in srgb, var(--primary-weak) 55%, transparent); }

.exbox {
  border: 1px solid var(--line); border-left: 5px solid var(--green); border-radius: 10px;
  background: var(--surface); margin: 16px 0; box-shadow: var(--shadow); overflow: hidden;
}
.ex-head { padding: 11px 16px 0; font-weight: 800; line-height: 1.6; }
.ex-head .badge { margin-right: 6px; vertical-align: 1px; }
.ex-q { padding: 4px 16px 10px; }
.ex-q p { margin: 6px 0; }
details.sol-toggle > summary {
  list-style: none; cursor: pointer; padding: 9px 16px; font-weight: 700; font-size: .9rem; color: var(--green);
  background: var(--green-weak); border-top: 1px solid var(--line); display: flex; align-items: center; gap: 8px; user-select: none;
}
details.sol-toggle > summary::-webkit-details-marker { display: none; }
details.sol-toggle > summary::before { content: "▸"; transition: transform .15s; }
details.sol-toggle[open] > summary::before { transform: rotate(90deg); }
details.sol-toggle > summary:hover { filter: brightness(.97); }
details.sol-toggle .ex-body { padding: 4px 18px 14px; }
details.sol-toggle .ex-body p { margin: 8px 0; }
details.sol-toggle.plain { border: 1px solid var(--line); border-radius: 10px; margin: 10px 0; overflow: hidden; background: var(--surface); }
details.sol-toggle.plain > summary { border-top: 0; background: var(--surface-2); color: var(--muted); }
.steps { counter-reset: s; list-style: none; padding-left: 0 !important; }
.steps > li { counter-increment: s; position: relative; padding-left: 34px; margin: 10px 0; }
.steps > li::before {
  content: counter(s); position: absolute; left: 0; top: 2px; width: 24px; height: 24px; border-radius: 50%;
  background: var(--green); color: #fff; font-size: .8rem; font-weight: 800; display: grid; place-items: center;
}
.ans { font-weight: 700; color: var(--green); }

.cheat { display: grid; grid-template-columns: repeat(auto-fit, minmax(260px, 1fr)); gap: 12px; margin-top: 12px; }
.cheat .card { padding: 12px 16px; }
.cheat h4 { margin: 0 0 4px; font-size: .95rem; color: var(--accent); }

/* widgets */
.widget { border: 1px solid var(--line); border-radius: var(--radius); background: var(--surface); padding: 14px 16px; margin: 16px 0; box-shadow: var(--shadow); }
.widget > .wt { font-weight: 800; font-size: .95rem; display: flex; align-items: center; gap: 8px; margin-bottom: 8px; }
.widget > .wt .badge { margin-left: auto; }
.wrow { display: flex; flex-wrap: wrap; gap: 10px 18px; align-items: center; margin: 6px 0; }
.wrow label { font-size: .88rem; color: var(--muted); display: flex; align-items: center; gap: 8px; }
.wrow input[type="range"] { width: 170px; accent-color: var(--primary); }
.wrow select, .wrow input[type="number"], .wrow input[type="text"] {
  font: inherit; padding: 6px 10px; border-radius: 8px; border: 1px solid var(--line); background: var(--bg); color: var(--text);
}
.seg { display: inline-flex; border: 1px solid var(--line); border-radius: 10px; overflow: hidden; }
.seg button { border: 0; background: var(--surface); padding: 6px 14px; font-weight: 700; font-size: .9rem; color: var(--muted); border-right: 1px solid var(--line); }
.seg button:last-child { border-right: 0; }
.seg button[aria-pressed="true"] { background: var(--primary); color: var(--primary-ink); }
.plots { display: grid; grid-template-columns: repeat(3, 1fr); gap: 10px; margin-top: 8px; }
@media (max-width: 720px) { .plots { grid-template-columns: 1fr; } }
.plot { border: 1px solid var(--line); border-radius: 10px; padding: 6px 8px 2px; background: var(--bg); }
.plot.hit { border-color: var(--green); background: var(--green-weak); }
.plot .pt { font-size: .8rem; font-weight: 700; color: var(--muted); }
.plot.hit .pt { color: var(--green); }
.plot svg { width: 100%; height: auto; display: block; }
.readout { font-variant-numeric: tabular-nums; font-size: .95rem; margin: 6px 0 0; }
.readout b { color: var(--primary); }
.phbar { height: 18px; border-radius: 9px; background: linear-gradient(90deg, #e5484d 0%, #f59e0b 25%, #84cc16 45%, #22c55e 50%, #38bdf8 62%, #3b5bdb 82%, #7048e8 100%); position: relative; margin: 8px 0 22px; }
.phbar i { position: absolute; top: -5px; width: 4px; height: 28px; background: var(--text); border-radius: 2px; transform: translateX(-2px); }
.phbar span { position: absolute; top: 24px; font-size: .7rem; color: var(--muted); transform: translateX(-50%); }
.qk { display: grid; grid-template-columns: 1fr; gap: 6px; margin-top: 8px; }
.qk .bar { height: 26px; border-radius: 6px; display: flex; align-items: center; padding: 0 10px; font-weight: 700; font-size: .82rem; color: #fff; transition: width .25s; min-width: 40px; white-space: nowrap; }
.qk .bar.q { background: #2f9e6f; } .qk .bar.k { background: #d04a4a; }

/* ---------- MEMORIZE ---------- */
.toolbar { display: flex; flex-wrap: wrap; gap: 10px 14px; align-items: center; margin-bottom: 14px; }
.toolbar .grp { display: flex; flex-wrap: wrap; gap: 6px; align-items: center; }
.toolbar .lbl { font-size: .78rem; font-weight: 800; letter-spacing: .06em; color: var(--muted); text-transform: uppercase; margin-right: 2px; }
.toolbar .spacer { flex: 1; }
.switch { display: inline-flex; align-items: center; gap: 8px; font-size: .88rem; color: var(--muted); cursor: pointer; user-select: none; }
.switch input { accent-color: var(--primary); width: 16px; height: 16px; }

.mem-stats { display: flex; gap: 14px; flex-wrap: wrap; align-items: center; font-size: .88rem; color: var(--muted); margin: 0 0 14px; }
.mem-stats b { color: var(--text); font-variant-numeric: tabular-nums; }
.progress { flex: 1 1 160px; height: 8px; border-radius: 4px; background: var(--surface-2); overflow: hidden; border: 1px solid var(--line); min-width: 120px; }
.progress > i { display: block; height: 100%; background: var(--green); width: 0; transition: width .3s; }

.stage { max-width: 760px; margin: 0 auto; }
.fc-wrap { perspective: 1400px; }
.flashcard {
  position: relative; display: grid; min-height: 320px; cursor: pointer; transform-style: preserve-3d; transition: transform .45s cubic-bezier(.3, .7, .3, 1);
}
.flashcard.flipped { transform: rotateY(180deg); }
.fc-face {
  grid-area: 1 / 1; backface-visibility: hidden; -webkit-backface-visibility: hidden;
  background: var(--surface); border: 1px solid var(--line); border-radius: 16px; box-shadow: var(--shadow); padding: 22px 26px;
  display: flex; flex-direction: column;
}
.fc-back { transform: rotateY(180deg); border-top: 5px solid var(--green); }
.fc-front { border-top: 5px solid var(--accent, var(--primary)); justify-content: center; }
.fc-meta { display: flex; gap: 6px; flex-wrap: wrap; margin-bottom: 12px; }
.fc-q { font-size: 1.3rem; font-weight: 700; line-height: 1.45; letter-spacing: -.01em; }
.fc-hint { margin-top: auto; padding-top: 16px; font-size: .82rem; color: var(--muted); text-align: center; }
.fc-back .en { font-size: 1.04rem; line-height: 1.7; }
.fc-back .ko { margin-top: 12px; padding-top: 10px; border-top: 1px dashed var(--line); color: var(--muted); font-size: .93rem; }
.key { background: color-mix(in srgb, var(--amber) 22%, transparent); border-radius: 4px; padding: 0 3px; font-weight: 700; box-decoration-break: clone; -webkit-box-decoration-break: clone; }
.fc-actions { display: flex; gap: 10px; justify-content: center; margin-top: 16px; flex-wrap: wrap; }
.fc-nav { display: flex; align-items: center; justify-content: space-between; gap: 10px; margin-top: 14px; font-size: .9rem; color: var(--muted); }
.kbd { font-family: var(--mono); font-size: .75rem; padding: 1px 6px; border-radius: 5px; border: 1px solid var(--line); background: var(--surface-2); }
.empty { text-align: center; padding: 40px 16px; color: var(--muted); }

.write-box textarea {
  width: 100%; min-height: 130px; resize: vertical; font: inherit; line-height: 1.6; padding: 12px 14px; border-radius: 10px;
  border: 1px solid var(--line); background: var(--bg); color: var(--text);
}
.write-box textarea:focus { outline: 3px solid color-mix(in srgb, var(--primary) 40%, transparent); border-color: var(--primary); }
.kw-list { display: flex; flex-wrap: wrap; gap: 6px; margin: 10px 0; }
.kw { font-size: .85rem; font-weight: 700; padding: 3px 10px; border-radius: 999px; border: 1px solid transparent; }
.kw.hit { background: var(--green-weak); color: var(--green); border-color: color-mix(in srgb, var(--green) 40%, transparent); }
.kw.miss { background: var(--red-weak); color: var(--red); border-color: color-mix(in srgb, var(--red) 40%, transparent); }
.score-line { font-weight: 800; font-size: 1.02rem; }
.model { margin-top: 12px; padding: 12px 16px; border-radius: 10px; background: var(--surface-2); border-left: 4px solid var(--green); }
.model .ko { margin-top: 8px; color: var(--muted); font-size: .93rem; }

.cloze-text { font-size: 1.08rem; line-height: 2.2; }
.blank {
  display: inline-block; min-width: 4.2em; padding: 0 8px; margin: 0 2px; border-radius: 6px; border: 0; border-bottom: 2px solid var(--primary);
  background: var(--primary-weak); color: transparent; cursor: pointer; font: inherit; line-height: 1.6; vertical-align: baseline; user-select: none; transition: all .15s;
}
.blank.open { color: var(--text); background: color-mix(in srgb, var(--amber) 22%, transparent); border-bottom-color: var(--amber); font-weight: 700; }

.clist { display: grid; gap: 8px; }
.clist details { background: var(--surface); border: 1px solid var(--line); border-radius: 10px; }
.clist summary { cursor: pointer; padding: 10px 14px; display: flex; gap: 8px; align-items: center; flex-wrap: wrap; list-style: none; font-weight: 600; }
.clist summary::-webkit-details-marker { display: none; }
.clist summary::before { content: "▸"; color: var(--muted); transition: transform .15s; }
.clist details[open] summary::before { transform: rotate(90deg); }
.clist .body { padding: 2px 16px 12px 30px; border-top: 1px dashed var(--line); }
.clist .body .ko { color: var(--muted); font-size: .92rem; margin-top: 6px; }
.search { flex: 1 1 220px; max-width: 360px; font: inherit; padding: 7px 12px; border-radius: 999px; border: 1px solid var(--line); background: var(--surface); color: var(--text); }
.dot { width: 10px; height: 10px; border-radius: 50%; background: var(--line); flex: none; }
.dot.known { background: var(--green); } .dot.unsure { background: var(--red); }

/* ---------- PRACTICE ---------- */
.p-layout { display: grid; grid-template-columns: minmax(0, 1fr) 260px; gap: 22px; align-items: start; }
@media (max-width: 960px) { .p-layout { grid-template-columns: minmax(0, 1fr); } .p-side { order: -1; } }
.p-side { position: sticky; top: 128px; display: grid; gap: 12px; }
@media (max-width: 960px) { .p-side { position: static; } }
.p-side .card { padding: 12px 14px; }
.p-side h4 { margin: 0 0 8px; font-size: .82rem; letter-spacing: .06em; text-transform: uppercase; color: var(--muted); }
.ring-row { display: grid; gap: 8px; }
.ring-row .r { display: grid; grid-template-columns: 62px 1fr auto; gap: 8px; align-items: center; font-size: .84rem; }
.ring-row .r span:last-child { font-variant-numeric: tabular-nums; color: var(--muted); }
.mode-seg { display: flex; flex-wrap: wrap; gap: 8px; margin-bottom: 14px; }
.mode-seg .btn { flex: 1 1 auto; text-align: center; }
.mode-seg .btn[aria-pressed="true"] { background: var(--primary); color: var(--primary-ink); border-color: var(--primary); }

.prob { background: var(--surface); border: 1px solid var(--line); border-radius: var(--radius); box-shadow: var(--shadow); padding: 16px 20px; margin-bottom: 16px; border-top: 4px solid var(--accent, var(--primary)); }
.prob.c13 { --accent: var(--c13); } .prob.c14 { --accent: var(--c14); } .prob.c15 { --accent: var(--c15); }
.prob.done-ok { border-color: color-mix(in srgb, var(--green) 55%, var(--line)); }
.prob.done-bad { border-color: color-mix(in srgb, var(--red) 55%, var(--line)); }
.prob-head { display: flex; gap: 6px; flex-wrap: wrap; align-items: center; margin-bottom: 8px; }
.prob-head .pid { font-weight: 800; font-size: .95rem; margin-right: 4px; }
.prob-head .state { margin-left: auto; font-size: .8rem; font-weight: 800; }
.prob-head .state.ok { color: var(--green); } .prob-head .state.bad { color: var(--red); }
.stem { margin: 6px 0 10px; }
.stem p { margin: 6px 0; }
.part { margin: 12px 0; padding: 10px 12px; background: var(--bg); border: 1px solid var(--line); border-radius: 10px; }
.part .plabel { font-weight: 800; color: var(--accent); margin-right: 6px; }
.opts { display: grid; gap: 6px; margin-top: 8px; }
.opt {
  display: flex; gap: 10px; align-items: flex-start; text-align: left; width: 100%;
  border: 1px solid var(--line); background: var(--surface); border-radius: 10px; padding: 8px 12px; transition: all .12s;
}
.opt:hover:not([disabled]) { border-color: var(--primary); background: var(--primary-weak); }
.opt > span:last-child { line-height: 2.3; min-width: 0; }
.opt .k { flex: none; width: 24px; height: 24px; border-radius: 50%; border: 1.5px solid var(--muted); display: grid; place-items: center; font-size: .78rem; font-weight: 800; color: var(--muted); }
.opt.right { border-color: var(--green); background: var(--green-weak); } .opt.right .k { background: var(--green); border-color: var(--green); color: #fff; }
.opt.wrong { border-color: var(--red); background: var(--red-weak); } .opt.wrong .k { background: var(--red); border-color: var(--red); color: #fff; }
.opt[disabled] { cursor: default; }
.numrow { display: flex; flex-wrap: wrap; gap: 8px; align-items: center; margin-top: 8px; }
.numrow input[type="text"] {
  font: inherit; font-family: var(--mono); font-size: .98rem; width: 190px; padding: 8px 12px; border-radius: 8px;
  border: 1px solid var(--line); background: var(--surface); color: var(--text);
}
.numrow .unit { color: var(--muted); font-size: .94rem; }
.fb { margin-top: 8px; font-size: .92rem; padding: 8px 12px; border-radius: 8px; }
.fb.ok { background: var(--green-weak); color: var(--green); }
.fb.bad { background: var(--red-weak); color: var(--red); }
.fb.info { background: var(--surface-2); color: var(--muted); }
.fb b { font-weight: 800; }
.prob-actions { display: flex; gap: 8px; flex-wrap: wrap; margin-top: 10px; }
.sol { margin-top: 12px; padding: 4px 16px 12px; border-radius: 10px; background: var(--surface-2); border-left: 4px solid var(--green); }
.sol h5 { margin: 10px 0 2px; font-size: .78rem; letter-spacing: .08em; color: var(--green); text-transform: uppercase; }
.self-row { display: flex; gap: 8px; flex-wrap: wrap; margin-top: 8px; }
.gen-bar { display: flex; flex-wrap: wrap; gap: 8px; align-items: center; margin-bottom: 14px; }
.gen-bar select { font: inherit; padding: 7px 10px; border-radius: 8px; border: 1px solid var(--line); background: var(--surface); color: var(--text); }
.score-banner { padding: 14px 18px; border-radius: var(--radius); background: var(--primary-weak); border: 1px solid color-mix(in srgb, var(--primary) 30%, transparent); margin-bottom: 14px; display: flex; align-items: center; gap: 14px; flex-wrap: wrap; }
.score-banner b { font-size: 1.3rem; }

footer.site-footer { max-width: 1120px; margin: 0 auto; padding: 0 16px 40px; color: var(--muted); font-size: .82rem; }
footer.site-footer hr { border: 0; border-top: 1px solid var(--line); margin: 0 0 14px; }

code { font-family: var(--mono); background: var(--surface-2); padding: 1px 6px; border-radius: 5px; font-size: .88em; }
.ptxt { margin-bottom: 2px; }
.study-main, .p-main { min-width: 0; }
.katex { font-size: 1.06em; }
.katex-display { overflow-x: auto; overflow-y: hidden; max-width: 100%; padding: 2px 0; }
.eq .katex-display { margin: .4em 0; }
@media (max-width: 520px) {
  main { padding-inline: 12px; }
  .toc { margin-inline: -12px; padding-inline: 12px; }
  .card { padding: 14px; }
  .fc-face { padding: 18px; }
  .fc-q { font-size: 1.15rem; }
  .flashcard { min-height: 360px; }
  .numrow input[type="text"] { width: 100%; }
}