/* ===========================================================
   07-280 Study Guide — shared stylesheet
   =========================================================== */

:root {
  --bg:        #fbfaf8;
  --bg-soft:   #f2f0ec;
  --panel:     #ffffff;
  --ink:       #1c1b19;
  --ink-soft:  #4a4844;
  --ink-mute:  #77746e;
  --line:      #e2ded7;
  --line-2:    #cdc8bf;

  --accent:    #b4501e;   /* terracotta   */
  --accent-2:  #1f6f6b;   /* deep teal    */
  --accent-3:  #6b4fa8;   /* violet       */
  --gold:      #a07d12;
  --rose:      #a8324a;

  --c-intuition: #1f6f6b;
  --c-analogy:   #6b4fa8;
  --c-key:       #b4501e;
  --c-proof:     #3b5c8a;
  --c-warn:      #a8324a;
  --c-example:   #a07d12;

  --radius: 10px;
  --shadow: 0 1px 2px rgba(28,27,25,.05), 0 6px 20px rgba(28,27,25,.05);
  --mono: ui-monospace, "SF Mono", "JetBrains Mono", Menlo, Consolas, monospace;
  --serif: "Iowan Old Style", "Palatino Linotype", Palatino, Georgia, serif;
  --sans: -apple-system, BlinkMacSystemFont, "Segoe UI", Inter, Helvetica, Arial, sans-serif;
}

@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    --bg:        #14151a;
    --bg-soft:   #1b1d24;
    --panel:     #1e2028;
    --ink:       #e9e7e2;
    --ink-soft:  #c2bfb8;
    --ink-mute:  #8d8a84;
    --line:      #2c2f38;
    --line-2:    #3b3f4a;

    --accent:    #e2864f;
    --accent-2:  #4fbcb4;
    --accent-3:  #a58ae0;
    --gold:      #d6ac3e;
    --rose:      #e4738a;

    --c-intuition: #4fbcb4;
    --c-analogy:   #a58ae0;
    --c-key:       #e2864f;
    --c-proof:     #7aa6dd;
    --c-warn:      #e4738a;
    --c-example:   #d6ac3e;

    --shadow: 0 1px 2px rgba(0,0,0,.3), 0 6px 20px rgba(0,0,0,.25);
  }
}
:root[data-theme="dark"] {
  --bg:#14151a; --bg-soft:#1b1d24; --panel:#1e2028;
  --ink:#e9e7e2; --ink-soft:#c2bfb8; --ink-mute:#8d8a84;
  --line:#2c2f38; --line-2:#3b3f4a;
  --accent:#e2864f; --accent-2:#4fbcb4; --accent-3:#a58ae0;
  --gold:#d6ac3e; --rose:#e4738a;
  --c-intuition:#4fbcb4; --c-analogy:#a58ae0; --c-key:#e2864f;
  --c-proof:#7aa6dd; --c-warn:#e4738a; --c-example:#d6ac3e;
  --shadow: 0 1px 2px rgba(0,0,0,.3), 0 6px 20px rgba(0,0,0,.25);
}

* { box-sizing: border-box; }

html { scroll-behavior: smooth; scroll-padding-top: 80px; }

body {
  margin: 0;
  background: var(--bg);
  color: var(--ink);
  font-family: var(--sans);
  font-size: 17px;
  line-height: 1.7;
  -webkit-font-smoothing: antialiased;
}

/* ---------- top bar ---------- */
.topbar {
  position: sticky; top: 0; z-index: 40;
  display: flex; align-items: center; gap: 14px;
  padding: 10px 20px;
  background: color-mix(in srgb, var(--bg) 88%, transparent);
  backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--line);
}
.topbar .brand {
  font-weight: 700; letter-spacing: -.02em; color: var(--ink);
  text-decoration: none; font-size: 15px; white-space: nowrap;
}
.topbar .brand span { color: var(--accent); }
.topbar .spacer { flex: 1; }
.topbar .crumb { color: var(--ink-mute); font-size: 14px; }
.iconbtn {
  border: 1px solid var(--line); background: var(--panel); color: var(--ink-soft);
  border-radius: 8px; padding: 5px 10px; font-size: 13px; cursor: pointer;
  font-family: inherit;
}
.iconbtn:hover { border-color: var(--line-2); color: var(--ink); }
#menuToggle { display: none; }

/* ---------- layout ---------- */
.shell { display: grid; grid-template-columns: 268px minmax(0,1fr); gap: 0; }

.sidebar {
  border-right: 1px solid var(--line);
  padding: 22px 16px 60px;
  position: sticky; top: 49px; align-self: start;
  height: calc(100vh - 49px); overflow-y: auto;
  background: var(--bg);
}
.sidebar h4 {
  font-size: 11px; text-transform: uppercase; letter-spacing: .12em;
  color: var(--ink-mute); margin: 20px 0 8px 10px; font-weight: 700;
}
.sidebar h4:first-child { margin-top: 0; }
.sidebar a {
  display: block; padding: 6px 10px; border-radius: 7px;
  color: var(--ink-soft); text-decoration: none; font-size: 14.5px;
  line-height: 1.4; margin-bottom: 1px;
}
.sidebar a:hover { background: var(--bg-soft); color: var(--ink); }
.sidebar a.active { background: color-mix(in srgb, var(--accent) 13%, transparent); color: var(--accent); font-weight: 600; }
.sidebar a .num { color: var(--ink-mute); font-variant-numeric: tabular-nums; margin-right: 7px; font-size: 12.5px; }
.sidebar a.active .num { color: var(--accent); }

main { padding: 38px 40px 100px; max-width: 860px; }

/* ---------- typography ---------- */
h1 {
  font-size: 2.35rem; line-height: 1.15; letter-spacing: -.028em;
  margin: 0 0 6px; font-weight: 750;
}
.subtitle { color: var(--ink-mute); font-size: 1.05rem; margin: 0 0 8px; }
.eyebrow {
  text-transform: uppercase; letter-spacing: .14em; font-size: 11.5px;
  font-weight: 700; color: var(--accent); margin-bottom: 10px;
}
h2 {
  font-size: 1.55rem; letter-spacing: -.02em; margin: 3rem 0 .8rem;
  padding-top: .4rem; font-weight: 700;
  border-top: 1px solid var(--line);
}
h2:first-of-type { border-top: none; }
h3 { font-size: 1.16rem; margin: 2rem 0 .6rem; font-weight: 680; letter-spacing: -.01em; }
h4 { font-size: 1rem; margin: 1.4rem 0 .4rem; font-weight: 650; color: var(--ink-soft); }
p { margin: 0 0 1rem; }
a { color: var(--accent); }
strong { font-weight: 660; }
ul, ol { margin: 0 0 1rem; padding-left: 1.35rem; }
li { margin-bottom: .4rem; }
li::marker { color: var(--ink-mute); }
hr { border: none; border-top: 1px solid var(--line); margin: 2.5rem 0; }
code {
  font-family: var(--mono); font-size: .875em;
  background: var(--bg-soft); padding: .12em .38em; border-radius: 5px;
  border: 1px solid var(--line);
}
pre {
  background: var(--bg-soft); border: 1px solid var(--line);
  border-radius: var(--radius); padding: 14px 16px; overflow-x: auto;
  font-size: 13.5px; line-height: 1.6;
}
pre code { background: none; border: none; padding: 0; font-size: inherit; }

/* ---------- callouts ---------- */
.box {
  border: 1px solid var(--line); border-left: 3px solid var(--ink-mute);
  background: var(--panel); border-radius: var(--radius);
  padding: 14px 18px; margin: 1.4rem 0; box-shadow: var(--shadow);
}
.box > :first-child { margin-top: 0; }
.box > :last-child { margin-bottom: 0; }
.box .label {
  display: block; font-size: 11px; font-weight: 750; letter-spacing: .13em;
  text-transform: uppercase; margin-bottom: 7px;
}
.box.intuition { border-left-color: var(--c-intuition); }
.box.intuition .label { color: var(--c-intuition); }
.box.analogy   { border-left-color: var(--c-analogy); }
.box.analogy .label { color: var(--c-analogy); }
.box.key       { border-left-color: var(--c-key); background: color-mix(in srgb, var(--accent) 6%, var(--panel)); }
.box.key .label { color: var(--c-key); }
.box.proof     { border-left-color: var(--c-proof); }
.box.proof .label { color: var(--c-proof); }
.box.warn      { border-left-color: var(--c-warn); }
.box.warn .label { color: var(--c-warn); }
.box.example   { border-left-color: var(--c-example); }
.box.example .label { color: var(--c-example); }
.box.defn      { border-left-color: var(--ink); }
.box.defn .label { color: var(--ink); }

/* ---------- guided problem ---------- */
.guided {
  border: 1px solid var(--line-2); border-radius: var(--radius);
  background: var(--panel); margin: 1.8rem 0; overflow: hidden;
  box-shadow: var(--shadow);
}
.guided > .g-head {
  background: var(--bg-soft); padding: 12px 18px;
  border-bottom: 1px solid var(--line); font-weight: 650;
}
.guided > .g-head .tag {
  display: inline-block; font-size: 10.5px; letter-spacing: .12em;
  text-transform: uppercase; color: var(--accent); font-weight: 750;
  margin-right: 10px;
}
.guided > .g-body { padding: 14px 18px; }
.guided > .g-body > :first-child { margin-top: 0; }

details.step {
  border-top: 1px solid var(--line); padding: 0;
}
details.step > summary {
  cursor: pointer; padding: 10px 18px; font-weight: 600; font-size: 15px;
  list-style: none; color: var(--accent-2); user-select: none;
}
details.step > summary::-webkit-details-marker { display: none; }
details.step > summary::before {
  content: "▸"; display: inline-block; margin-right: 9px;
  transition: transform .15s ease; color: var(--ink-mute);
}
details.step[open] > summary::before { transform: rotate(90deg); }
details.step > summary:hover { background: var(--bg-soft); }
details.step > div { padding: 2px 18px 14px 40px; }
details.step > div > :first-child { margin-top: 0; }
details.step > div > :last-child { margin-bottom: 0; }

/* ---------- tables ---------- */
table {
  border-collapse: collapse; width: 100%; margin: 1.3rem 0;
  font-size: 15px; font-variant-numeric: tabular-nums;
}
th, td { border: 1px solid var(--line); padding: 7px 11px; text-align: left; }
th { background: var(--bg-soft); font-weight: 650; font-size: 13.5px; }
tbody tr:nth-child(even) td { background: color-mix(in srgb, var(--bg-soft) 45%, transparent); }
table.tight { width: auto; }
table.center td, table.center th { text-align: center; }
.scroll-x { overflow-x: auto; }

/* ---------- visualizations ---------- */
.viz {
  border: 1px solid var(--line); border-radius: var(--radius);
  background: var(--panel); padding: 16px 18px; margin: 1.6rem 0;
  box-shadow: var(--shadow);
}
.viz .viz-title {
  font-size: 11px; text-transform: uppercase; letter-spacing: .13em;
  font-weight: 750; color: var(--ink-mute); margin-bottom: 12px;
}
.viz .caption { font-size: 14px; color: var(--ink-mute); margin-top: 10px; }
.controls { display: flex; flex-wrap: wrap; gap: 14px; align-items: center; margin: 12px 0 4px; }
.controls label { font-size: 13.5px; color: var(--ink-soft); display: flex; align-items: center; gap: 8px; }
.controls input[type=range] { accent-color: var(--accent); width: 150px; }
.controls .val { font-family: var(--mono); font-size: 13px; color: var(--accent); min-width: 44px; }
button.btn {
  border: 1px solid var(--line-2); background: var(--bg-soft); color: var(--ink);
  border-radius: 8px; padding: 6px 13px; font-size: 14px; cursor: pointer;
  font-family: inherit; font-weight: 550;
}
button.btn:hover { border-color: var(--accent); color: var(--accent); }
button.btn.primary { background: var(--accent); color: #fff; border-color: var(--accent); }
button.btn.primary:hover { filter: brightness(1.08); color: #fff; }
svg { max-width: 100%; height: auto; display: block; }
svg text { font-family: var(--sans); }

/* ---------- quiz ---------- */
.quiz { border: 1px solid var(--line); border-radius: var(--radius); background: var(--panel); padding: 14px 18px; margin: 1.5rem 0; }
.quiz .q { font-weight: 620; margin-bottom: 10px; }
.quiz .opt {
  display: block; width: 100%; text-align: left; border: 1px solid var(--line);
  background: var(--bg); border-radius: 8px; padding: 8px 12px; margin-bottom: 7px;
  cursor: pointer; font: inherit; font-size: 15px; color: var(--ink);
}
.quiz .opt:hover { border-color: var(--line-2); }
.quiz .opt.right { border-color: var(--c-intuition); background: color-mix(in srgb, var(--c-intuition) 12%, var(--bg)); }
.quiz .opt.wrong { border-color: var(--c-warn); background: color-mix(in srgb, var(--c-warn) 10%, var(--bg)); }
.quiz .why { font-size: 14.5px; color: var(--ink-soft); margin-top: 8px; display: none; }
.quiz .why.show { display: block; }

/* ---------- misc components ---------- */
.grid2 { display: grid; grid-template-columns: 1fr 1fr; gap: 16px; }
.grid3 { display: grid; grid-template-columns: repeat(3,1fr); gap: 14px; }
@media (max-width: 720px) { .grid2, .grid3 { grid-template-columns: 1fr; } }

.card {
  border: 1px solid var(--line); border-radius: var(--radius); background: var(--panel);
  padding: 16px 18px; box-shadow: var(--shadow); text-decoration: none; color: inherit;
  display: block;
}
a.card:hover { border-color: var(--accent); }
.card h3 { margin: 0 0 6px; font-size: 1.05rem; }
.card p { margin: 0; font-size: 14.5px; color: var(--ink-mute); }
.card .kicker { font-size: 11px; letter-spacing: .12em; text-transform: uppercase; color: var(--accent); font-weight: 750; }

.pill {
  display: inline-block; font-size: 12px; padding: 2px 9px; border-radius: 999px;
  border: 1px solid var(--line-2); color: var(--ink-mute); margin-right: 6px;
}

.pagenav {
  display: flex; justify-content: space-between; gap: 14px;
  margin-top: 4rem; padding-top: 1.4rem; border-top: 1px solid var(--line);
}
.pagenav a {
  text-decoration: none; color: var(--ink-soft); font-size: 14.5px;
  border: 1px solid var(--line); border-radius: var(--radius); padding: 10px 16px;
  background: var(--panel); flex: 1;
}
.pagenav a:hover { border-color: var(--accent); color: var(--accent); }
.pagenav a .lbl { display: block; font-size: 11px; text-transform: uppercase; letter-spacing: .12em; color: var(--ink-mute); }
.pagenav a.next { text-align: right; }

.toc {
  border: 1px solid var(--line); border-radius: var(--radius); background: var(--bg-soft);
  padding: 14px 18px; margin: 1.6rem 0 2.4rem; font-size: 15px;
}
.toc .t { font-size: 11px; text-transform: uppercase; letter-spacing: .13em; font-weight: 750; color: var(--ink-mute); margin-bottom: 8px; }
.toc ol { margin: 0; padding-left: 1.2rem; columns: 2; column-gap: 28px; }
@media (max-width: 720px) { .toc ol { columns: 1; } }
.toc li { margin-bottom: 3px; }
.toc a { text-decoration: none; color: var(--ink-soft); }
.toc a:hover { color: var(--accent); text-decoration: underline; }

.katex-display { margin: 1.2rem 0 !important; overflow-x: auto; overflow-y: hidden; padding: 2px 0; }
.katex { font-size: 1.04em; }

.muted { color: var(--ink-mute); }
.tiny { font-size: 13.5px; }
.center { text-align: center; }

/* ---------- mobile ---------- */
@media (max-width: 900px) {
  body { font-size: 16px; }
  .shell { grid-template-columns: 1fr; }
  #menuToggle { display: inline-block; }
  .sidebar {
    position: fixed; top: 49px; left: 0; width: 280px; z-index: 50;
    transform: translateX(-102%); transition: transform .2s ease;
    box-shadow: 0 0 40px rgba(0,0,0,.25);
  }
  .sidebar.open { transform: translateX(0); }
  main { padding: 24px 16px 80px; }
  h1 { font-size: 1.85rem; }
  h2 { font-size: 1.32rem; }
}