:root {
      --bg: #f3f4fb;
      --bg-soft: #eef0fa;
      --ink: #131b31;
      --muted: #6f788d;
      --border: rgba(19, 27, 49, 0.12);
      --panel: rgba(255, 255, 255, 0.7);
      --curve: #b6a48f;
      --hex: #1f4c48;
      --point: #c94b4b;
      --guide-one: rgba(112, 128, 170, 0.34);
      --guide-two: rgba(138, 120, 164, 0.34);
      --guide-three: rgba(128, 156, 118, 0.34);
      --pascal: #c96544;
      --shadow: 0 22px 70px rgba(42, 54, 96, 0.12);
    }

    * {
      box-sizing: border-box;
    }

    html,
    body {
      margin: 0;
      min-height: 100%;
      width: 100%;
    }

    body {
      overflow: hidden;
      background:
        radial-gradient(circle at 18% 12%, rgba(255, 255, 255, 0.92), transparent 26%),
        radial-gradient(circle at 82% 18%, rgba(116, 146, 255, 0.08), transparent 24%),
        radial-gradient(circle at 72% 78%, rgba(201, 101, 68, 0.08), transparent 22%),
        linear-gradient(180deg, var(--bg), var(--bg-soft));
      color: var(--ink);
      font-family: "Lexend", "Avenir Next", "SF Pro Display", "Helvetica Neue", sans-serif;
    }

    .app {
      position: relative;
      width: 100vw;
      height: 100vh;
      overflow: hidden;
    }

    .topbar {
      position: absolute;
      top: 26px;
      right: 26px;
      z-index: 30;
      display: flex;
      gap: 12px;
    }

    .pill {
      border: 1px solid rgba(19, 27, 49, 0.14);
      background: rgba(255, 255, 255, 0.9);
      color: var(--ink);
      border-radius: 999px;
      min-width: 64px;
      height: 64px;
      padding: 0 20px;
      display: inline-flex;
      align-items: center;
      justify-content: center;
      font: inherit;
      font-size: 0.98rem;
      font-weight: 700;
      letter-spacing: -0.03em;
      box-shadow: 0 10px 26px rgba(42, 54, 96, 0.08);
      cursor: pointer;
      transition: transform 180ms ease, border-color 180ms ease, background 180ms ease, box-shadow 180ms ease;
    }

    .pill:hover {
      transform: translateY(-1px);
      box-shadow: 0 14px 30px rgba(42, 54, 96, 0.1);
    }

    .pill.active {
      border-color: rgba(19, 27, 49, 0.48);
      background: rgba(255, 255, 255, 0.98);
    }

    .pill.hidden {
      opacity: 0;
      pointer-events: none;
      transform: translateY(-10px);
    }

    .pill-lang {
      gap: 8px;
      min-width: 92px;
      height: 56px;
      padding: 0 16px 0 12px;
      justify-content: flex-start;
      letter-spacing: -0.04em;
      border-color: rgba(19, 27, 49, 0.1);
      background: rgba(255, 255, 255, 0.78);
      box-shadow: 0 8px 22px rgba(42, 54, 96, 0.06);
    }

    .pill-lang.active {
      border-color: rgba(19, 27, 49, 0.22);
      background: rgba(255, 255, 255, 0.88);
      box-shadow: 0 10px 24px rgba(42, 54, 96, 0.08);
    }

    .pill-lang-badge {
      width: 28px;
      height: 28px;
      border-radius: 999px;
      display: inline-flex;
      align-items: center;
      justify-content: center;
      background: rgba(19, 27, 49, 0.05);
      color: currentColor;
      flex: 0 0 auto;
      box-shadow: inset 0 0 0 1px rgba(19, 27, 49, 0.04);
    }

    .pill-lang.active .pill-lang-badge {
      background: rgba(19, 27, 49, 0.07);
      box-shadow: inset 0 0 0 1px rgba(19, 27, 49, 0.06);
    }

    .pill-lang-text {
      display: inline-flex;
      align-items: baseline;
      gap: 7px;
      line-height: 1;
    }

    .pill-lang-code {
      font-size: 0.96rem;
      font-weight: 800;
      letter-spacing: -0.04em;
    }

    .pill-lang-label {
      display: none;
    }

    .pill-lang.active .pill-lang-label {
      color: rgba(19, 27, 49, 0.78);
    }

    .pill-icon {
      width: 17px;
      height: 17px;
      display: inline-block;
      color: currentColor;
      flex: 0 0 auto;
    }

    #home-button .pill-icon {
      width: 22px;
      height: 22px;
    }

    #home-button {
      width: 56px;
      min-width: 56px;
      height: 56px;
      padding: 0;
    }

    .lang-copy {
      transition: opacity 240ms cubic-bezier(0.22, 1, 0.36, 1);
      will-change: opacity;
    }

    .app.language-transitioning .lang-copy {
      opacity: 0.08;
    }

    .hero {
      position: absolute;
      inset: 0;
      z-index: 20;
      display: grid;
      place-items: center;
      padding: 40px;
      transition: opacity 500ms ease, transform 500ms ease;
    }

    .hero.hidden {
      opacity: 0;
      transform: translateY(-24px);
      pointer-events: none;
    }

    .hero-inner {
      width: min(1120px, 100%);
      display: grid;
      grid-template-columns: minmax(0, 1fr) minmax(260px, 360px);
      gap: 36px;
      align-items: center;
      text-align: left;
    }

    .hero-copy {
      min-width: 0;
      transform: translateX(24px);
    }

    .eyebrow {
      margin: 0 0 18px;
      color: var(--muted);
      font-size: clamp(0.78rem, 1vw, 0.92rem);
      font-weight: 600;
      letter-spacing: 0;
    }

    .title {
      margin: 0;
      font-size: clamp(2.8rem, 6.8vw, 5.8rem);
      line-height: 0.92;
      letter-spacing: -0.065em;
      font-weight: 800;
      max-width: 9ch;
    }

    html[lang="ko"] .title {
      max-width: 7.2ch;
      line-height: 1.02;
      letter-spacing: -0.045em;
      word-break: keep-all;
    }

    .subtitle {
      margin: 22px 0 0;
      max-width: 31ch;
      color: var(--muted);
      font-size: clamp(0.98rem, 1.45vw, 1.32rem);
      line-height: 1.58;
      letter-spacing: -0.035em;
    }

    .hero-actions {
      margin-top: 28px;
      display: flex;
      flex-wrap: wrap;
      gap: 14px;
    }

    .action {
      height: 58px;
      padding: 0 22px;
      border-radius: 18px;
      border: 1px solid rgba(19, 27, 49, 0.12);
      background: rgba(255, 255, 255, 0.86);
      color: var(--muted);
      font: inherit;
      font-size: 0.96rem;
      font-weight: 700;
      letter-spacing: -0.025em;
      box-shadow: 0 10px 26px rgba(42, 54, 96, 0.08);
      cursor: pointer;
      display: inline-flex;
      align-items: center;
      gap: 10px;
      transition: transform 180ms ease, box-shadow 180ms ease, border-color 180ms ease;
    }

    .action.primary {
      color: var(--ink);
      border: 2px solid rgba(19, 27, 49, 0.46);
      background: rgba(255, 255, 255, 0.92);
    }

    .action:hover {
      transform: translateY(-1px);
      box-shadow: 0 14px 30px rgba(42, 54, 96, 0.1);
    }

    .action:active,
    .pill:active,
    .nav:active {
      transform: translateY(0) scale(0.985);
    }

    .action-icon {
      width: 18px;
      height: 18px;
      display: inline-block;
      color: currentColor;
      flex: 0 0 auto;
    }

    .hero-figure {
      display: flex;
      justify-content: flex-start;
      align-items: center;
      margin-left: -132px;
    }

    .hero-image {
      width: min(140%, 620px);
      max-height: 70vh;
      object-fit: contain;
      filter: drop-shadow(0 20px 42px rgba(42, 54, 96, 0.14));
      user-select: none;
      pointer-events: none;
      transform: translateX(-92px);
    }

    .stage {
      position: absolute;
      inset: 0;
      display: grid;
      place-items: center;
      padding: 26px 26px 248px;
    }

    .diagram-shell {
      width: min(94vw, 94vh);
      height: min(94vw, 94vh);
      transition: transform 900ms cubic-bezier(0.22, 1, 0.36, 1), opacity 400ms ease;
      transform-origin: center center;
      opacity: 0;
    }

    .diagram-shell.visible {
      opacity: 1;
    }

    svg {
      width: 100%;
      height: 100%;
      display: block;
      overflow: visible;
    }

    .caption {
      position: absolute;
      left: 50%;
      bottom: 52px;
      transform: translateX(-50%);
      z-index: 25;
      width: min(900px, calc(100vw - 48px));
      text-align: center;
      pointer-events: none;
      transition: opacity 280ms ease, transform 280ms ease;
    }

    .caption.hidden {
      opacity: 0;
      transform: translateX(-50%) translateY(16px);
    }

    .caption-box {
      opacity: 0;
      transform: translateY(18px);
      transition: opacity 320ms ease, transform 320ms ease;
    }

    .caption-box.visible {
      opacity: 1;
      transform: translateY(0);
    }

    .caption-step {
      display: block;
      margin-bottom: 10px;
      color: rgba(19, 27, 49, 0.56);
      font-size: clamp(0.72rem, 0.9vw, 0.86rem);
      font-weight: 700;
      letter-spacing: 0.16em;
      text-transform: uppercase;
    }

    .caption-title {
      display: block;
      font-size: clamp(1.04rem, 1.4vw, 1.42rem);
      line-height: 1.24;
      font-weight: 800;
      letter-spacing: -0.04em;
    }

    .caption-text {
      display: block;
      margin-top: 10px;
      color: var(--muted);
      font-size: clamp(0.92rem, 1.1vw, 1.08rem);
      line-height: 1.52;
      letter-spacing: -0.03em;
    }

    .controls {
      position: absolute;
      left: 50%;
      bottom: 170px;
      transform: translateX(-50%);
      z-index: 25;
      display: flex;
      gap: 12px;
      align-items: center;
      transition: opacity 280ms ease, transform 280ms ease;
    }

    .controls.hidden {
      opacity: 0;
      transform: translateX(-50%) translateY(16px);
      pointer-events: none;
    }

    .side-legend {
      position: absolute;
      left: 34px;
      top: 50%;
      transform: translateY(-50%);
      z-index: 25;
      width: min(280px, calc(100vw - 48px));
      display: grid;
      gap: 10px;
      transition: opacity 280ms ease, transform 280ms ease;
    }

    .side-legend.hidden {
      opacity: 0;
      transform: translateY(calc(-50% + 16px));
      pointer-events: none;
    }

    .side-legend-title {
      color: rgba(19, 27, 49, 0.5);
      font-size: 0.78rem;
      font-weight: 700;
      letter-spacing: 0.12em;
      text-transform: uppercase;
    }

    .side-legend-item {
      display: flex;
      align-items: center;
      gap: 10px;
      color: var(--muted);
      font-size: 0.92rem;
      font-weight: 600;
      letter-spacing: -0.02em;
      opacity: 0;
      transform: translateX(-8px);
      transition: opacity 260ms ease, transform 260ms ease;
    }

    .side-legend-item.visible {
      opacity: 1;
      transform: translateX(0);
    }

    .nav {
      width: 52px;
      height: 52px;
      padding: 0;
      border-radius: 18px;
      border: 1px solid rgba(19, 27, 49, 0.12);
      background: rgba(255, 255, 255, 0.86);
      color: var(--muted);
      font: inherit;
      font-size: 0.96rem;
      font-weight: 700;
      box-shadow: 0 10px 26px rgba(42, 54, 96, 0.08);
      cursor: pointer;
      display: inline-flex;
      align-items: center;
      justify-content: center;
      transition: transform 180ms ease, box-shadow 180ms ease, border-color 180ms ease, opacity 180ms ease, color 180ms ease;
    }

    .nav:hover:not(:disabled) {
      transform: translateY(-1px);
      box-shadow: 0 14px 30px rgba(42, 54, 96, 0.1);
      border-color: rgba(19, 27, 49, 0.2);
      color: var(--ink);
    }

    .nav:disabled {
      opacity: 0.45;
      cursor: default;
    }

    .nav .action-icon {
      width: 16px;
      height: 16px;
    }

    .randomize-button {
      height: 52px;
      padding: 0 18px;
      border-radius: 18px;
      font-size: 0.92rem;
      gap: 8px;
    }

    .randomize-button.hidden {
      display: none;
    }

    .outro {
      position: absolute;
      inset: 0;
      z-index: 24;
      display: grid;
      place-items: center;
      padding: 40px;
      opacity: 0;
      pointer-events: none;
      transform: translateY(20px);
      transition: opacity 420ms ease, transform 420ms ease;
    }

    .outro.visible {
      opacity: 1;
      pointer-events: auto;
      transform: translateY(0);
    }

    .outro-inner {
      width: min(1140px, 100%);
      display: grid;
      grid-template-columns: minmax(0, 420px) minmax(280px, 360px);
      gap: 48px;
      align-items: start;
    }

    .outro-copy {
      min-width: 0;
    }

    .outro-title {
      margin: 0;
      max-width: 10ch;
      font-size: clamp(2.6rem, 6.1vw, 5rem);
      line-height: 0.94;
      letter-spacing: -0.06em;
      font-weight: 800;
    }

    .outro-subtitle {
      margin: 20px 0 0;
      max-width: 34ch;
      color: var(--muted);
      font-size: clamp(0.96rem, 1.35vw, 1.24rem);
      line-height: 1.58;
      letter-spacing: -0.03em;
    }

    .sources {
      margin: 26px 0 0;
      padding: 0;
      list-style: none;
      display: grid;
      gap: 12px;
      max-width: 680px;
    }

    .sources a {
      display: inline-flex;
      align-items: center;
      gap: 10px;
      text-decoration: none;
      color: var(--muted);
      font-size: 1rem;
      font-weight: 500;
      letter-spacing: -0.02em;
      transition: color 180ms ease, transform 180ms ease;
    }

    .sources a:hover {
      color: var(--ink);
      transform: translateX(2px);
    }

    .source-dot {
      width: 8px;
      height: 8px;
      border-radius: 999px;
      background: rgba(19, 27, 49, 0.24);
      flex: 0 0 auto;
    }

    .outro-actions {
      margin-top: 30px;
      display: flex;
      flex-wrap: wrap;
      gap: 14px;
    }

    .legend-line {
      width: 34px;
      height: 0;
      border-top-width: 3px;
      border-top-style: solid;
      flex: 0 0 auto;
      border-radius: 999px;
    }

    .legend-line.curve {
      border-top-color: var(--curve);
    }

    .legend-line.hex {
      border-top-color: var(--hex);
    }

    .legend-line.guide {
      border-top-color: rgba(112, 128, 170, 0.72);
    }

    .legend-line.pascal {
      border-top-color: var(--pascal);
    }

    .outro-side {
      display: flex;
      flex-direction: column;
      align-items: flex-start;
      justify-content: flex-start;
      padding-top: 46px;
    }

    @media (max-width: 780px) {
      .topbar {
        top: 18px;
        right: 18px;
      }

      .pill {
        min-width: 56px;
        height: 56px;
        padding: 0 14px;
      }

      .pill-lang {
        min-width: 84px;
        height: 50px;
        padding: 0 14px 0 10px;
      }

      #home-button {
        width: 50px;
        min-width: 50px;
        height: 50px;
      }

      .pill-lang-badge {
        width: 24px;
        height: 24px;
      }

      .pill-lang-code {
        font-size: 0.88rem;
      }

      .hero {
        padding: 28px 22px 120px;
      }

      .hero-inner {
        grid-template-columns: 1fr;
        text-align: left;
      }

      .hero-copy {
        transform: translateX(14px);
      }

      .hero-figure {
        margin-left: -40px;
      }

      .hero-image {
        width: min(114%, 500px);
        transform: translateX(-32px);
      }

      .title {
        max-width: none;
      }

      html[lang="ko"] .title {
        max-width: 8.5ch;
        line-height: 1.06;
      }

      .hero-actions {
        gap: 10px;
      }

      .action {
        height: 54px;
        padding: 0 18px;
        border-radius: 18px;
      }

      .diagram-shell {
        width: 100vw;
        height: 100vw;
        max-height: 68vh;
      }

      .controls {
        bottom: 154px;
      }

      .caption {
        bottom: 44px;
      }

      .nav {
        width: 48px;
        height: 48px;
        border-radius: 16px;
      }

      .randomize-button {
        height: 48px;
        padding: 0 14px;
        border-radius: 16px;
        font-size: 0.86rem;
      }

      .side-legend {
        left: 22px;
        top: 50%;
        transform: translateY(-50%);
        width: min(220px, calc(100vw - 24px));
      }

      .stage {
        padding: 18px 18px 228px;
      }

      .outro {
        padding: 28px 22px;
      }

      .outro-inner {
        grid-template-columns: 1fr;
        gap: 24px;
      }

      .outro-side {
        padding-top: 0;
      }
    }