:root {
  color-scheme: light;
  --ink: #182724;
  --muted: #66736f;
  --paper: #ffffff;
  --card: #ffffff;
  --line: #d9ddd7;
  --grid: #e8e9e4;
  --teal: #0072b2;
  --teal-dark: #005a8c;
  --teal-soft: #d9edf7;
  --coral: #d55e00;
  --gold: #e69f00;
  --focus: #0072b2;
}

* { box-sizing: border-box; }

html { background: var(--paper); }

body {
  margin: 0;
  color: var(--ink);
  background: var(--paper);
  font-family: Inter, ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
  -webkit-font-smoothing: antialiased;
}

a { color: inherit; }
.course-title { display: flex; flex-direction: column; color: var(--ink); font-size: 1.05rem; font-weight: 750; line-height: 1.05; text-decoration: none; }
.course-title small { margin-top: 4px; color: var(--muted); font-size: 0.68rem; font-weight: 500; }
.top-actions { display: flex; align-items: center; gap: 10px; }
.top-link { padding: 8px 12px; color: var(--ink); background: #e5e7eb; border-radius: 7px; font-size: 0.8rem; font-weight: 700; line-height: 1; text-decoration: none; }
.top-link:hover { background: #d1d5db; }

.site-header {
  height: 62px;
  padding: 0 clamp(20px, 5vw, 72px);
  display: flex;
  align-items: center;
  justify-content: space-between;
  border-bottom: 1px solid rgba(24, 39, 36, 0.1);
}

.brand {
  display: inline-flex;
  gap: 11px;
  align-items: center;
  color: var(--ink);
  text-decoration: none;
  font-weight: 700;
  letter-spacing: -0.02em;
}

.brand-mark {
  width: 25px;
  height: 25px;
  display: inline-block;
  border: 2px solid var(--teal);
  border-radius: 50%;
  position: relative;
}

.brand-mark::before,
.brand-mark::after {
  content: "";
  position: absolute;
  background: var(--teal);
  transform-origin: 2px 2px;
}

.brand-mark::before { width: 10px; height: 2px; left: 11px; top: 10px; transform: rotate(-40deg); }
.brand-mark::after { width: 4px; height: 4px; left: 9px; top: 9px; border-radius: 50%; }

main { width: min(1180px, calc(100% - 32px)); margin: 0 auto; padding: 22px 0 20px; }

.intro { max-width: 820px; }
.title-row { display: flex; align-items: center; gap: 22px; }
.demo-qr { flex: 0 0 auto; line-height: 0; }
.demo-qr img { width: 112px; height: 112px; display: block; }
h1 { margin: 0; font-family: Georgia, "Times New Roman", serif; font-size: clamp(2.2rem, 4vw, 3.7rem); font-weight: 500; line-height: 0.98; letter-spacing: -0.045em; }
.book-reference { margin-top: 8px; display: inline-block; color: var(--muted); font-size: 0.78rem; text-underline-offset: 3px; }

.equation-card {
  margin-top: 14px;
  min-height: 62px;
  padding: 10px clamp(14px, 3vw, 24px);
  display: flex;
  gap: 24px;
  align-items: center;
  justify-content: space-between;
  background: var(--card);
  color: var(--ink);
  border: 1px solid var(--line);
  border-radius: 8px;
  overflow-x: auto;
}

.equation-main { font-size: clamp(0.92rem, 1.6vw, 1.15rem); white-space: nowrap; }

.control-panel {
  margin-top: 10px;
  padding: 12px 16px;
  display: grid;
  grid-template-columns: auto minmax(220px, 1.4fr) repeat(3, minmax(170px, 1fr));
  gap: 10px 18px;
  align-items: center;
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: 8px;
}

.transport { display: flex; gap: 12px; align-items: center; }
.play-button { width: 42px; height: 42px; padding: 0; display: grid; place-items: center; color: white; background: var(--teal); border: 0; border-radius: 50%; cursor: pointer; transition: transform 160ms ease, background 160ms ease; }
.play-button:hover { background: var(--teal-dark); transform: scale(1.04); }
.play-button:focus-visible, input:focus-visible, a:focus-visible { outline: 3px solid var(--focus); outline-offset: 3px; }
.play-button svg { width: 22px; height: 22px; fill: currentColor; }
.play-button .pause-icon { display: none; }
.play-button[aria-pressed="true"] .play-icon { display: none; }
.play-button[aria-pressed="true"] .pause-icon { display: block; }
.time-readout { min-width: 76px; display: flex; flex-direction: column; gap: 3px; }
.control-name { color: var(--muted); font-size: 0.74rem; font-weight: 700; text-transform: uppercase; letter-spacing: 0.08em; }
output { font-variant-numeric: tabular-nums; }
.time-readout output { font-weight: 800; }
.slider-control { min-width: 0; }
.slider-control label, .slider-control .control-label { margin-bottom: 11px; display: flex; justify-content: space-between; gap: 14px; font-size: 0.84rem; font-weight: 700; }
.slider-control .control-label label { margin: 0; display: inline; }
.slider-control label output, .slider-control .control-label output { color: var(--teal-dark); white-space: nowrap; }
.frequency-actions { display: inline-flex; align-items: center; gap: 9px; }
.frequency-actions button { padding: 5px 8px; color: var(--ink); background: #e5e7eb; border: 0; border-radius: 6px; font-family: inherit; font-size: 0.68rem; font-weight: 700; white-space: nowrap; cursor: pointer; }
.frequency-actions button:hover { background: #d1d5db; }
input[type="range"] { width: 100%; margin: 0; accent-color: var(--teal); cursor: pointer; }
.range-ends { margin-top: 5px; display: flex; justify-content: space-between; color: var(--muted); font-size: 0.68rem; }
.option-row { grid-column: 1 / -1; display: flex; gap: 22px; align-items: center; justify-content: space-between; }
.view-control { min-width: 0; margin: 0; padding: 0; display: flex; align-items: center; border: 0; }
.view-control legend { float: left; margin-right: 10px; color: var(--muted); font-size: 0.7rem; font-weight: 800; letter-spacing: 0.06em; text-transform: uppercase; }
.view-control label { cursor: pointer; }
.view-control input { position: absolute; opacity: 0; pointer-events: none; }
.view-control span { min-width: 68px; padding: 6px 12px; display: block; color: var(--muted); background: #f2f4f3; border: 1px solid var(--line); font-size: 0.75rem; font-weight: 750; text-align: center; }
.view-control label:first-of-type span { border-radius: 6px 0 0 6px; }
.view-control label:last-child span { border-radius: 0 6px 6px 0; }
.view-control label + label span { border-left: 0; }
.view-control input:checked + span { color: white; background: var(--teal); border-color: var(--teal); }
.view-control input:focus-visible + span { position: relative; z-index: 1; outline: 3px solid var(--focus); outline-offset: 2px; }
.period-control { display: flex; gap: 9px; align-items: center; color: var(--ink); font-size: 0.8rem; font-weight: 700; cursor: pointer; }
.period-control input { width: 17px; height: 17px; accent-color: var(--teal); }
.period-control output { margin-left: auto; color: var(--teal-dark); }

.visual-grid { height: clamp(220px, calc(100vh - 517px), 356px); margin-top: 10px; display: grid; grid-template-columns: minmax(260px, 0.82fr) minmax(380px, 1.35fr); gap: 10px; }
.plot-card { min-width: 0; min-height: 0; padding: 14px; background: var(--card); border: 1px solid var(--line); border-radius: 8px; overflow: hidden; }
.plot-heading { min-height: 48px; display: flex; align-items: flex-start; justify-content: space-between; gap: 16px; }
.plot-heading h2 { margin: 0; font-family: Georgia, "Times New Roman", serif; font-size: 1.55rem; font-weight: 500; letter-spacing: -0.025em; }

.canvas-wrap { position: relative; width: 100%; }
.phasor-wrap { max-width: 360px; height: calc(100% - 76px); min-height: 190px; margin: 2px auto 0; aspect-ratio: 1 / 1; }
.signal-wrap { margin-top: 2px; height: calc(100% - 78px); min-height: 190px; }
canvas { width: 100%; height: 100%; display: block; }
.axis-label { position: absolute; color: var(--muted); font-family: Georgia, "Times New Roman", serif; font-size: 0.82rem; font-style: italic; pointer-events: none; }
.axis-real { right: 4%; top: 48%; }
.axis-imaginary { left: 52%; top: 2%; }
.signal-y { left: 1px; top: 3%; transform: rotate(-90deg) translateX(-100%); transform-origin: 0 0; }
.signal-x { right: 2%; bottom: 0; }
.phasor-time-label { position: absolute; left: 7px; top: 7px; padding: 3px 6px; color: var(--ink); background: rgba(255, 255, 255, 0.9); border-radius: 4px; font-size: 0.68rem; font-weight: 700; font-variant-numeric: tabular-nums; pointer-events: none; }
.time-marker-label { position: absolute; top: 8px; padding: 4px 7px; color: var(--ink); background: rgba(255, 253, 248, 0.92); border: 1px solid var(--line); border-radius: 5px; font-size: 0.68rem; font-weight: 700; white-space: nowrap; pointer-events: none; transform: translateX(-50%); }
.period-label { position: absolute; top: 34px; padding: 3px 6px; color: var(--ink); background: rgba(255, 255, 255, 0.92); border-radius: 4px; font-size: 0.68rem; font-weight: 700; white-space: nowrap; pointer-events: none; transform: translateX(-50%); }

.sample-values { display: flex; gap: 12px; font-size: 0.75rem; }
.sample-values span { color: var(--muted); }
.sample-values strong { margin-left: 3px; color: var(--ink); font-variant-numeric: tabular-nums; }
.plot-footer { min-height: 26px; margin-top: 9px; display: flex; flex-wrap: wrap; gap: 14px 20px; align-items: center; color: var(--muted); font-size: 0.73rem; }
.plot-footer > span { display: inline-flex; gap: 7px; align-items: center; }
.phasor-legend { gap: 8px 12px; }
.plot-footer .cancellation-note { margin-left: auto; color: var(--ink); font-size: 0.68rem; font-weight: 650; font-variant-numeric: tabular-nums; }
.legend-dot { width: 8px; height: 8px; display: inline-block; border-radius: 50%; }
.current-dot { background: var(--teal); }
.legend-line { width: 19px; height: 3px; display: inline-block; }
.start-line { background: repeating-linear-gradient(90deg, var(--gold) 0 4px, transparent 4px 7px); }
.real-line { background: var(--teal); }
.imaginary-line { background: var(--coral); }
.site-footer { padding: 0 20px 14px; color: var(--muted); font-size: 0.72rem; text-align: center; }

@media (max-width: 900px) {
  .control-panel { grid-template-columns: auto 1fr 1fr; }
  .time-control { grid-column: 2 / 4; grid-row: 1; }
  .transport { grid-row: 1; }
  .option-row { grid-column: 1 / -1; }
  .visual-grid { grid-template-columns: minmax(220px, 0.8fr) minmax(330px, 1.2fr); }
}

@media (max-width: 650px) {
  .site-header { height: auto; padding-top: 12px; padding-bottom: 12px; align-items: flex-start; flex-direction: column; gap: 10px; }
  .top-actions { width: 100%; }
  .top-link { flex: 1; text-align: center; }
  main { width: min(100% - 16px, 1180px); padding: 14px 0 10px; }
  h1 { font-size: 2rem; }
  .book-reference { margin-top: 5px; font-size: 0.68rem; }
  .equation-card { min-height: 40px; margin-top: 8px; padding: 5px 9px; gap: 2px; font-size: 0.78rem; }
  .control-panel { margin-top: 8px; padding: 9px; grid-template-columns: auto 1fr 1fr; gap: 8px 10px; }
  .time-control { grid-column: 2; }
  .slider-control:not(.time-control) { grid-column: auto; }
  .frequency-control { grid-column: 1 / -1 !important; }
  .transport { grid-row: 1; }
  .transport .control-name { display: none; }
  .slider-control label, .slider-control .control-label { margin-bottom: 3px; font-size: 0.7rem; }
  .slider-control .control-label label { margin: 0; }
  .range-ends { display: none; }
  .option-row { gap: 8px; }
  .view-control legend { display: none; }
  .view-control span { min-width: 42px; padding: 5px 7px; font-size: 0.68rem; }
  .period-control { font-size: 0.68rem; }
  .period-control output { display: none; }
  .frequency-actions { gap: 6px; }
  .frequency-actions button { padding: 3px 5px; }
  .visual-grid { height: 190px; margin-top: 8px; grid-template-columns: minmax(0, 0.8fr) minmax(0, 1.2fr); gap: 6px; }
  .plot-card { padding: 7px; }
  .plot-heading { min-height: 26px; }
  .plot-heading h2 { font-size: 0.95rem; }
  .phasor-wrap, .signal-wrap { height: 125px; min-height: 0; margin-top: 0; }
  .sample-values { flex-direction: column; gap: 3px; }
  .sample-values { display: none; }
  .plot-footer { display: none; }
  .axis-label { font-size: 0.62rem; }
  .site-footer { padding-bottom: 8px; }
}

@media (max-width: 720px) { .demo-qr { display: none; } }

@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after { scroll-behavior: auto !important; transition: none !important; }
}