/* ==========================================================================
   01006030 Calculus 1 — OpenCourseWare style sheet
   Layout and component system adapted from an open lecture-notes template.
   ========================================================================== */

:root {
  /* Brand palette. The two bright accents fail contrast as text on white
     (#FF9100 = 2.3:1, #00B7CD = 2.4:1), so each has a darkened twin used
     wherever the colour carries words rather than decoration. */
  --red:        #DF301C;
  --red-dark:   #B22616;
  --orange:     #FF9100;
  --orange-ink: #A85E00;
  --cream:      #FFF1D1;
  --cream-soft: #FFF9EC;
  --cyan:       #00B7CD;
  --cyan-ink:   #00788A;

  --ink:        #1c1917;
  --ink-2:      #4b4540;
  --ink-3:      #726b64;
  --rule:       #e3dac7;
  --rule-soft:  #f2ecdd;
  --bg:         #ffffff;
  --bg-alt:     var(--cream);
  --bg-panel:   var(--cream-soft);
  --brand:      var(--red);
  --brand-dark: var(--red-dark);
  --link:       var(--cyan-ink);
  --link-hover: var(--red);
  --black:      #17120f;
  --note:       var(--cyan-ink);
  --warn:       var(--orange-ink);

  --sans: "Segoe UI", Roboto, "Helvetica Neue", Arial, "Noto Sans", sans-serif;
  --thai: "Noto Sans Thai", "IBM Plex Sans Thai", Sarabun, "Leelawadee UI", Tahoma, var(--sans);
  --mathfont: "Cambria Math", Cambria, "Times New Roman", Georgia, serif;
  --mono: "Cascadia Mono", Consolas, "SF Mono", Menlo, monospace;

  --maxw: 1220px;
  --sidebar: 300px;
}

* { box-sizing: border-box; }

/* Every size below is in rem, so the root drives the whole page. Thai gets a
   little more than Latin at the same nominal size: its glyphs sit smaller and
   the tone marks above and below need the extra room. Percentages rather than
   px so a reader's own browser font setting still applies. */
html {
  scroll-behavior: smooth;
  font-size: 112%;
}
html[lang="th"] { font-size: 118%; }

body {
  margin: 0;
  background: var(--bg);
  color: var(--ink);
  font-family: var(--sans);
  font-size: 1rem;
  line-height: 1.72;
  -webkit-font-smoothing: antialiased;
}

img, svg { max-width: 100%; }

a { color: var(--link); text-decoration: none; }
a:hover { color: var(--link-hover); text-decoration: underline; }

/* ---------------------------------------------------------------- topbar */

.topbar {
  background: var(--black);
  color: #fff;
  border-bottom: 3px solid var(--brand);
}

.topbar-inner {
  max-width: var(--maxw);
  margin: 0 auto;
  padding: 12px 24px;
  display: flex;
  align-items: center;
  gap: 20px;
  flex-wrap: wrap;
}

.logo {
  display: flex;
  align-items: center;
  gap: 10px;
  color: #fff;
  font-weight: 700;
  letter-spacing: .2px;
  font-size: 1.02rem;
}
.logo:hover { color: #fff; text-decoration: none; }

.logo-mark {
  display: inline-grid;
  place-items: center;
  width: 34px; height: 34px;
  background: var(--brand);
  color: #fff;
  font-weight: 800;
  font-size: .82rem;
  letter-spacing: .5px;
  border-radius: 2px;
}

.logo-text small {
  display: block;
  font-weight: 400;
  font-size: .68rem;
  letter-spacing: 1.4px;
  text-transform: uppercase;
  color: #b9b9b9;
}

.topbar-spacer { flex: 1 1 auto; }

.topbar-nav {
  display: flex;
  gap: 20px;
  font-size: .85rem;
}
.topbar-nav a { color: #d9d9d9; }
.topbar-nav a:hover { color: #fff; }

.lang-switch {
  display: inline-flex;
  border: 1px solid #4d4d4d;
  border-radius: 2px;
  overflow: hidden;
}
.lang-switch a {
  padding: 6px 13px;
  font-size: .78rem;
  font-weight: 700;
  letter-spacing: .3px;
  color: #cfcfcf;
  line-height: 1.5;
}
.lang-switch a + a { border-left: 1px solid #4d4d4d; }
.lang-switch a:hover { background: #2b2b2b; color: #fff; text-decoration: none; }
.lang-switch a.active { background: #fff; color: #111; }
.lang-switch a.active:hover { background: #fff; color: #111; }

.btn-give {
  background: var(--brand);
  color: #fff;
  padding: 7px 16px;
  border-radius: 2px;
  font-size: .82rem;
  font-weight: 700;
  letter-spacing: .3px;
}
.btn-give:hover { background: var(--brand-dark); color: #fff; text-decoration: none; }

/* -------------------------------------------------------- course masthead */

.masthead {
  background: var(--bg-alt);
  border-bottom: 1px solid var(--rule);
}

.masthead-inner {
  max-width: var(--maxw);
  margin: 0 auto;
  padding: 26px 24px 24px;
}

.eyebrow {
  font-size: .78rem;
  letter-spacing: 1.1px;
  text-transform: uppercase;
  color: var(--ink-3);
  font-weight: 600;
}
.eyebrow span { color: var(--orange); }

.masthead h1 {
  margin: 8px 0 0;
  font-size: 2.35rem;
  line-height: 1.15;
  letter-spacing: -.4px;
  font-weight: 700;
}

.masthead .tagline {
  margin: 10px 0 0;
  color: var(--ink-2);
  max-width: 68ch;
}

/* ----------------------------------------------------------------- layout */

.layout {
  max-width: var(--maxw);
  margin: 0 auto;
  padding: 0 24px 64px;
  display: grid;
  grid-template-columns: var(--sidebar) minmax(0, 1fr);
  gap: 48px;
  align-items: start;
}

/* ---------------------------------------------------------------- sidebar */

.sidebar { padding-top: 28px; }

.course-menu { border-top: 2px solid var(--ink); }

.course-menu h2,
.course-info h2 {
  font-size: .78rem;
  letter-spacing: 1.2px;
  text-transform: uppercase;
  color: var(--ink-3);
  margin: 14px 0 10px;
  font-weight: 700;
}

.course-menu ul {
  list-style: none;
  margin: 0;
  padding: 0;
}

.course-menu li { border-bottom: 1px solid var(--rule-soft); }

.course-menu a,
.course-menu .muted {
  display: block;
  padding: 11px 4px;
  font-size: .97rem;
  color: var(--ink);
}
.course-menu a:hover { color: var(--brand); text-decoration: none; }

.course-menu a.active {
  color: var(--brand);
  font-weight: 700;
  box-shadow: inset 3px 0 0 var(--brand);
  padding-left: 12px;
}

.course-menu .muted {
  color: #a5a5a5;
  cursor: default;
}
.course-menu .muted em {
  font-style: normal;
  font-size: .72rem;
  color: #b5b5b5;
  display: block;
}

.course-info {
  margin-top: 34px;
  background: var(--bg-panel);
  border: 1px solid var(--rule);
  padding: 18px 18px 6px;
}

.course-info dl { margin: 0; }
.course-info dt {
  font-size: .74rem;
  letter-spacing: .8px;
  text-transform: uppercase;
  color: var(--ink-3);
  font-weight: 700;
  margin-top: 14px;
}
.course-info dd {
  margin: 3px 0 0;
  font-size: .95rem;
  color: var(--ink);
}
.course-info dd ul {
  margin: 0; padding: 0; list-style: none;
}
.course-info dd li { padding: 1px 0; }
.course-info .crumbs { color: var(--ink-2); font-size: .86rem; }

/* ----------------------------------------------------------------- content */

.content { padding-top: 32px; min-width: 0; }

.content h2 {
  font-size: 1.5rem;
  margin: 42px 0 12px;
  padding-bottom: 8px;
  border-bottom: 2px solid var(--rule);
  line-height: 1.25;
  scroll-margin-top: 20px;
}
.content > h2:first-child { margin-top: 0; }

.content h3 {
  font-size: 1.16rem;
  margin: 30px 0 8px;
  color: var(--ink);
  scroll-margin-top: 20px;
}

.content h4 {
  font-size: 1rem;
  margin: 22px 0 6px;
  color: var(--ink-2);
  text-transform: uppercase;
  letter-spacing: .6px;
  font-size: .87rem;
}

.content p { margin: 0 0 17px; }

.content ul, .content ol { margin: 0 0 18px; padding-left: 24px; }
.content li { margin-bottom: 8px; }

/* Cap the measure. At the larger base size the column would otherwise run to
   nearly 100 characters per line, which tires the eye as much as small type. */
.content p,
.content ul,
.content ol { max-width: 76ch; }
.toc ol { max-width: none; }

.lead {
  font-size: 1.1rem;
  color: var(--ink-2);
  border-left: 3px solid var(--brand);
  padding-left: 16px;
  margin-bottom: 26px;
}

/* --------------------------------------------------------- in-page toc box */

.toc {
  background: var(--bg-panel);
  border: 1px solid var(--rule);
  padding: 16px 20px;
  margin-bottom: 30px;
}
.toc h2 {
  border: 0;
  margin: 0 0 8px;
  font-size: .8rem;
  letter-spacing: 1.2px;
  text-transform: uppercase;
  color: var(--ink-3);
  padding: 0;
}
.toc ol {
  columns: 2;
  column-gap: 32px;
  margin: 0;
  padding-left: 20px;
  font-size: .95rem;
}
.toc li { margin-bottom: 3px; break-inside: avoid; }

/* ------------------------------------------------------------------ tables */

.table-wrap { overflow-x: auto; margin: 0 0 8px; }

table {
  border-collapse: collapse;
  width: 100%;
  font-size: .93rem;
}

caption {
  caption-side: top;
  text-align: left;
  font-size: .88rem;
  color: var(--ink-2);
  padding-bottom: 8px;
}
caption b { color: var(--ink); }

th, td {
  border-bottom: 1px solid var(--rule-soft);
  padding: 11px 14px;
  text-align: left;
  vertical-align: top;
}

thead th {
  background: var(--bg-panel);
  border-bottom: 2px solid var(--rule);
  font-size: .82rem;
  letter-spacing: .4px;
  text-transform: uppercase;
  color: var(--ink-2);
  white-space: nowrap;
}

tbody tr:hover { background: var(--cream-soft); }

td.num, th.num { text-align: right; font-variant-numeric: tabular-nums; }

/* ---------------------------------------------------------------- formulas */

.eq {
  display: flex;
  align-items: center;
  gap: 16px;
  margin: 18px 0;
  padding: 14px 18px;
  background: var(--bg-panel);
  border-left: 3px solid var(--cyan);
  font-family: var(--mathfont);
  font-size: 1.15rem;
  overflow-x: auto;
}
.eq .body { flex: 1 1 auto; }
.eq .tag {
  flex: 0 0 auto;
  font-family: var(--sans);
  font-size: .82rem;
  color: var(--ink-3);
}

var, .v {
  font-family: var(--mathfont);
  font-style: italic;
}

.frac {
  display: inline-block;
  vertical-align: middle;
  text-align: center;
  margin: 0 4px;
}
.frac > span { display: block; padding: 0 6px; line-height: 1.3; }
.frac .den { border-top: 1.4px solid currentColor; }

.units { font-family: var(--sans); font-size: .86rem; color: var(--ink-3); }

/* Piecewise ("cases") definitions, e.g. |x| = x if x >= 0, -x if x < 0 */
.cases {
  display: inline-flex;
  align-items: center;
  gap: 10px;
  vertical-align: middle;
  margin: 0 4px;
}
.cases .brace {
  font-size: 2.6em;
  line-height: 1;
  font-family: var(--mathfont);
  color: currentColor;
}
.cases .rows {
  display: grid;
  grid-template-columns: auto auto;
  column-gap: 22px;
  row-gap: 8px;
  font-size: .92em;
}
.cases .rows .v { text-align: right; }
.cases .rows .cond { text-align: left; color: var(--ink-2); font-family: var(--sans); font-style: normal; font-size: .86em; }

/* A stack of individually-numbered equations that belong to one family
   (e.g. the three ratios sin, cos, tan) reads as one visually grouped block */
.eq-group { margin: 18px 0; }
.eq-group .eq { margin: 0; border-radius: 0; }
.eq-group .eq + .eq { border-top: 1px solid var(--rule); margin-top: -1px; }

/* ---------------------------------------------------------------- callouts */

.callout {
  border: 1px solid var(--rule);
  border-left: 4px solid var(--cyan);
  background: #f0fafc;
  padding: 14px 18px;
  margin: 20px 0;
  font-size: 1rem;
}
.callout.warn { border-left-color: var(--orange); background: #fff6e4; }
.callout.rule { border-left-color: var(--brand); background: #fdf1ef; }
.callout p:last-child { margin-bottom: 0; }
.callout .label {
  display: block;
  font-size: .74rem;
  letter-spacing: 1px;
  text-transform: uppercase;
  font-weight: 700;
  color: var(--note);
  margin-bottom: 5px;
}
.callout.warn .label { color: var(--warn); }
.callout.rule .label { color: var(--brand); }

/* ----------------------------------------------------------------- figures */

figure {
  margin: 26px 0;
  border: 1px solid var(--rule);
  background: #fff;
  padding: 18px;
}
figure svg { display: block; width: 100%; height: auto; }
figcaption {
  margin-top: 12px;
  font-size: .9rem;
  color: var(--ink-2);
  border-top: 1px solid var(--rule-soft);
  padding-top: 10px;
}
figcaption b { color: var(--ink); }

/* -------------------------------------------------------- worked example */

.example {
  border: 1px solid var(--rule);
  border-top: 4px solid var(--cyan);
  padding: 4px 24px 18px;
  margin: 26px 0;
  background: #fffdf8;
}
.example h3 { margin-top: 20px; }
.step {
  margin: 18px 0;
  padding-left: 16px;
  border-left: 2px solid var(--rule);
}
.step > h4 { margin-top: 0; color: var(--brand); }

.result {
  display: inline-block;
  background: #fff;
  border: 1.5px solid var(--ink);
  padding: 6px 14px;
  font-family: var(--mathfont);
  font-size: 1.08rem;
  margin: 6px 0;
}

/* ------------------------------------------------------------ misc content */

.cards {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(230px, 1fr));
  gap: 18px;
  margin: 22px 0;
}
.card {
  border: 1px solid var(--rule);
  padding: 16px 18px;
  background: #fff;
}
.card h3 { margin: 0 0 6px; font-size: 1rem; }
.card p { font-size: .94rem; color: var(--ink-2); margin: 0; }

.chapter-nav {
  display: flex;
  justify-content: space-between;
  gap: 16px;
  margin-top: 52px;
  padding-top: 18px;
  border-top: 2px solid var(--rule);
  font-size: .96rem;
}

.pill {
  display: inline-block;
  background: var(--bg-alt);
  border: 1px solid var(--rule);
  border-radius: 999px;
  padding: 2px 11px;
  font-size: .76rem;
  color: var(--ink-2);
  margin: 0 4px 4px 0;
}

.refs { font-size: .95rem; }
.refs li { margin-bottom: 10px; }

/* -------------------------------------------------------------------- quiz */

.quiz-status {
  position: sticky;
  top: 0;
  z-index: 5;
  background: var(--bg);
  border-bottom: 2px solid var(--rule);
  padding: 12px 0 10px;
  margin-bottom: 22px;
  display: flex;
  align-items: center;
  gap: 20px;
  flex-wrap: wrap;
  font-size: .95rem;
  color: var(--ink-2);
}
.quiz-status b { color: var(--ink); font-size: 1.05rem; font-variant-numeric: tabular-nums; }

.quiz-meter {
  flex: 1 1 160px;
  min-width: 110px;
  height: 8px;
  background: var(--rule-soft);
  border-radius: 999px;
  overflow: hidden;
}
.quiz-meter i { display: block; height: 100%; width: 0; background: var(--cyan); transition: width .25s; }

.quiz-item {
  border: 1px solid var(--rule);
  border-left: 4px solid var(--rule);
  background: #fff;
  padding: 18px 22px;
  margin: 0 0 18px;
  scroll-margin-top: 70px;
}
.quiz-item.is-correct { border-left-color: var(--cyan); }
.quiz-item.is-wrong   { border-left-color: var(--brand); }
.quiz-item.is-shown   { border-left-color: var(--orange); }

.quiz-head { display: flex; gap: 12px; align-items: baseline; flex-wrap: wrap; }
.quiz-no { font-weight: 700; color: var(--ink-3); font-variant-numeric: tabular-nums; }
.quiz-q { font-weight: 600; flex: 1 1 20ch; max-width: 74ch; }

.quiz-ref {
  flex: 0 0 auto;
  font-size: .8rem;
  font-weight: 700;
  background: var(--bg-alt);
  border: 1px solid var(--rule);
  border-radius: 999px;
  padding: 3px 12px;
  white-space: nowrap;
}

.quiz-opts { list-style: none; margin: 14px 0 0; padding: 0; max-width: 76ch; }
.quiz-opts li { margin: 0 0 8px; }

.quiz-opt {
  display: flex;
  gap: 11px;
  align-items: flex-start;
  border: 1px solid var(--rule);
  padding: 10px 14px;
  cursor: pointer;
  background: #fff;
}
.quiz-opt:hover { background: var(--cream-soft); }
.quiz-opt input { margin: .35em 0 0; flex: 0 0 auto; }
.quiz-opt .k { font-weight: 700; color: var(--ink-3); flex: 0 0 1.5em; }
.quiz-opt .tx { flex: 1 1 auto; }

/* Locked questions keep full contrast; only the radio itself greys out */
.quiz-item.locked .quiz-opt { cursor: default; color: var(--ink); }
.quiz-item.locked .quiz-opt:hover { background: #fff; }
.quiz-opt.correct { border-color: var(--cyan); background: #f0fafc; }
.quiz-opt.correct .k { color: var(--cyan-ink); }
.quiz-opt.wrong { border-color: var(--brand); background: #fdf1ef; }
.quiz-opt.wrong .k { color: var(--brand); }
.quiz-item.locked .quiz-opt.correct:hover { background: #f0fafc; }
.quiz-item.locked .quiz-opt.wrong:hover { background: #fdf1ef; }

.quiz-mark { flex: 0 0 auto; font-weight: 700; font-size: .84rem; white-space: nowrap; }
.quiz-opt.correct .quiz-mark { color: var(--cyan-ink); }
.quiz-opt.wrong .quiz-mark { color: var(--brand); }

.quiz-why {
  margin-top: 15px;
  border-top: 1px solid var(--rule-soft);
  padding-top: 13px;
  font-size: .95rem;
  max-width: 76ch;
}
.quiz-why .lab {
  font-weight: 700;
  color: var(--cyan-ink);
  text-transform: uppercase;
  font-size: .76rem;
  letter-spacing: .8px;
  display: block;
  margin-bottom: 4px;
}

.quiz-actions { display: flex; gap: 12px; flex-wrap: wrap; margin: 26px 0 0; }
.quiz-btn {
  border: 1.5px solid var(--ink);
  background: #fff;
  color: var(--ink);
  font: inherit;
  font-size: .92rem;
  font-weight: 700;
  padding: 9px 18px;
  border-radius: 2px;
  cursor: pointer;
}
.quiz-btn:hover { background: var(--ink); color: #fff; }
.quiz-btn.primary { background: var(--brand); border-color: var(--brand); color: #fff; }
.quiz-btn.primary:hover { background: var(--brand-dark); border-color: var(--brand-dark); }

.quiz-result {
  border: 1px solid var(--rule);
  border-top: 4px solid var(--cyan);
  background: var(--bg-panel);
  padding: 20px 24px;
  margin: 26px 0 0;
}
.quiz-result h3 { margin: 0 0 6px; }
.quiz-score { font-size: 1.9rem; font-weight: 700; line-height: 1.2; }
.quiz-score small { font-size: .95rem; font-weight: 400; color: var(--ink-2); }
.quiz-weak { margin-top: 12px; font-size: .95rem; }
.quiz-weak a { margin-right: 10px; font-weight: 600; white-space: nowrap; }

.quiz-noscript {
  border: 1px solid var(--rule);
  border-left: 4px solid var(--brand);
  background: #fdf1ef;
  padding: 14px 18px;
  margin-bottom: 22px;
}

/* ------------------------------------------------------------------ footer */

.site-footer {
  background: var(--black);
  color: #b7b7b7;
  padding: 40px 24px 30px;
  font-size: .9rem;
}
.footer-inner {
  max-width: var(--maxw);
  margin: 0 auto;
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
  gap: 28px;
}
.site-footer h3 {
  color: #fff;
  font-size: .78rem;
  letter-spacing: 1.2px;
  text-transform: uppercase;
  margin: 0 0 10px;
}
.site-footer a { color: #cfcfcf; }
.site-footer a:hover { color: #fff; }
.site-footer ul { list-style: none; margin: 0; padding: 0; }
.site-footer li { margin-bottom: 6px; }
.footer-bottom {
  max-width: var(--maxw);
  margin: 30px auto 0;
  padding-top: 18px;
  border-top: 1px solid #333;
  color: #8d8d8d;
  font-size: .8rem;
}

/* ------------------------------------------------------- Thai typography */

html[lang="th"] body {
  font-family: var(--thai);
  line-height: 1.9;
}
html[lang="th"] .masthead h1 { line-height: 1.35; letter-spacing: 0; }
html[lang="th"] .content h2,
html[lang="th"] .content h3 { line-height: 1.5; }
html[lang="th"] .content li { margin-bottom: 8px; }
html[lang="th"] table { line-height: 1.75; }
html[lang="th"] thead th,
html[lang="th"] .eyebrow,
html[lang="th"] .course-menu h2,
html[lang="th"] .course-info dt,
html[lang="th"] .callout .label,
html[lang="th"] .content h4,
html[lang="th"] .site-footer h3 { letter-spacing: .2px; }

/* Latin-script fragments inside Thai pages keep the Latin stack */
html[lang="th"] .eq,
html[lang="th"] var,
html[lang="th"] .v,
html[lang="th"] .result { font-family: var(--mathfont); }
html[lang="th"] .units,
html[lang="th"] .eq .tag { font-family: var(--thai); }

/* -------------------------------------------------------------- responsive */

/* The department line is long enough to wrap the header on mid-width screens */
@media (max-width: 1150px) {
  .logo-text small { display: none; }
}

@media (max-width: 900px) {
  .layout {
    grid-template-columns: minmax(0, 1fr);
    gap: 8px;
  }
  .sidebar { order: 2; padding-top: 8px; }
  .content { order: 1; }
  .masthead h1 { font-size: 1.85rem; }
  .toc ol { columns: 1; }
  .topbar-nav { display: none; }
}

@media (max-width: 520px) {
  /* Ease off at phone width, but stay above the old 16px baseline */
  html { font-size: 106%; }
  html[lang="th"] { font-size: 112%; }
  .layout, .masthead-inner, .topbar-inner { padding-left: 16px; padding-right: 16px; }
  .example { padding-left: 14px; padding-right: 14px; }
  th, td { padding: 9px 10px; }
}

/* ------------------------------------------------------------------- print */

@media print {
  .topbar, .sidebar, .site-footer, .chapter-nav, .toc { display: none; }
  .layout { display: block; padding: 0; }
  body { font-size: 11pt; }
  figure, table, .eq, .example { break-inside: avoid; }
  a { color: #000; text-decoration: none; }
}