/*
 * Pass 4 — application styles.
 * Vanilla CSS: cascade layers, semantic tokens, OKLCH, native nesting.
 * Tokens live in @layer base; extend them rather than hardcoding values.
 */

@layer reset, base, components, utilities;

@layer reset {
  *, *::before, *::after { box-sizing: border-box; }
  body, h1, h2, h3, p, ol, ul, dl, dd, fieldset, figure { margin: 0; }
  img { max-width: 100%; display: block; }
}

@layer base {
  :root {
    color-scheme: light dark;

    /* Warm-neutral grays; no blue cast */
    --color-surface: oklch(98.5% 0.003 90);
    --color-text: oklch(24% 0.006 90);
    --color-text-muted: oklch(47% 0.006 90);
    --color-text-subtle: oklch(60% 0.005 90);
    --color-border: oklch(25% 0.01 90 / 0.14);
    --color-border-strong: oklch(25% 0.01 90 / 0.28);
    --color-hover-wash: oklch(25% 0.01 90 / 0.05);

    --color-accent: oklch(50% 0.1 200);
    --color-correct: oklch(52% 0.12 150);
    --color-incorrect: oklch(54% 0.17 25);
    --color-fill-contrast: oklch(99% 0 0);

    --text-xs: 0.75rem;
    --text-sm: 0.875rem;
    --text-base: 1rem;
    --text-lg: 1.125rem;
    --text-xl: 1.375rem;
    --text-2xl: 1.875rem;

    --line-height-tight: 1.25;
    --line-height-normal: 1.5;
    --line-height-relaxed: 1.625;

    --space-1: 0.25rem;
    --space-2: 0.5rem;
    --space-3: 0.75rem;
    --space-4: 1rem;
    --space-5: 1.5rem;
    --space-6: 2rem;
    --space-8: 3rem;
    --space-10: 4rem;

    --radius-md: 0.5rem;
    --radius-full: 9999px;

    --duration-fast: 150ms;
    --duration-reveal: 250ms;
    --ease-standard: cubic-bezier(0.4, 0, 0.2, 1);
    --ease-pop: cubic-bezier(0.34, 1.56, 0.64, 1);
  }

  @media (prefers-color-scheme: dark) {
    :root {
      --color-surface: oklch(19% 0.004 90);
      --color-text: oklch(91% 0.004 90);
      --color-text-muted: oklch(69% 0.005 90);
      --color-text-subtle: oklch(56% 0.005 90);
      --color-border: oklch(100% 0 0 / 0.1);
      --color-border-strong: oklch(100% 0 0 / 0.2);
      --color-hover-wash: oklch(100% 0 0 / 0.05);

      --color-accent: oklch(76% 0.09 200);
      --color-correct: oklch(75% 0.13 150);
      --color-incorrect: oklch(72% 0.15 25);
      --color-fill-contrast: oklch(20% 0.004 90);
    }
  }

  body {
    max-width: 40rem;
    margin-inline: auto;
    padding-inline: var(--space-4);
    background: var(--color-surface);
    color: var(--color-text);
    font-family: ui-sans-serif, system-ui, sans-serif;
    font-size: var(--text-base);
    line-height: var(--line-height-normal);
  }

  h1 {
    font-size: var(--text-xl);
    font-weight: 600;
    line-height: var(--line-height-tight);
    letter-spacing: -0.01em;
    margin-block-end: var(--space-4);
  }

  h2 {
    font-size: var(--text-lg);
    font-weight: 600;
    line-height: var(--line-height-tight);
    margin-block: var(--space-6) var(--space-3);
  }

  p { max-width: 36em; }

  a { color: var(--color-accent); }

  :focus-visible {
    outline: 2px solid var(--color-accent);
    outline-offset: 2px;
  }

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

@layer components {
  /* --- Shell: chrome sits directly on the page background --- */

  .site-header {
    display: flex;
    align-items: baseline;
    justify-content: space-between;
    padding-block: var(--space-4);
    border-block-end: 1px solid var(--color-border);

    .brand {
      font-weight: 600;
      color: var(--color-text);
      text-decoration: none;
    }

    nav {
      display: flex;
      gap: var(--space-4);
      align-items: baseline;

      form { display: contents; }
    }

    nav a {
      font-size: var(--text-sm);
      color: var(--color-text-muted);
      text-decoration: none;

      &:hover { color: var(--color-text); }
    }
  }

  .flash {
    padding: var(--space-3) var(--space-4);
    margin-block-end: var(--space-4);
    border: 1px solid color-mix(in oklab, var(--color-incorrect) 40%, transparent);
    border-radius: var(--radius-md);
    background: color-mix(in oklab, var(--color-incorrect) 7%, transparent);
    font-size: var(--text-sm);

    &.notice {
      border-color: color-mix(in oklab, var(--color-correct) 40%, transparent);
      background: color-mix(in oklab, var(--color-correct) 7%, transparent);
    }
  }

  main { padding-block: var(--space-6) var(--space-10); }

  .breadcrumb {
    font-size: var(--text-sm);
    margin-block-end: var(--space-4);

    a {
      color: var(--color-text-subtle);
      text-decoration: none;

      &:hover { color: var(--color-text); text-decoration: underline; }
    }
  }

  .meta {
    font-size: var(--text-sm);
    color: var(--color-text-muted);
  }

  /* --- Home --- */

  .hero {
    padding-block: var(--space-8);

    h1 { font-size: var(--text-2xl); }

    p { color: var(--color-text-muted); }

    .button { margin-block-start: var(--space-5); }
  }

  /* --- Buttons: one family, pyramid of emphasis --- */

  .button, button, input[type="submit"] {
    display: inline-flex;
    align-items: center;
    padding: var(--space-2) var(--space-4);
    border: 1px solid transparent;
    border-radius: var(--radius-md);
    background: var(--color-accent);
    color: var(--color-fill-contrast);
    font: inherit;
    font-size: var(--text-sm);
    font-weight: 500;
    text-decoration: none;
    cursor: pointer;
    transition: background-color var(--duration-fast) var(--ease-standard),
                border-color var(--duration-fast) var(--ease-standard),
                scale var(--duration-fast) var(--ease-standard);

    &:hover {
      background: color-mix(in oklab, var(--color-accent) 86%, var(--color-text));
    }

    &:active { scale: 0.97; }

    &.secondary {
      background: transparent;
      border-color: var(--color-border-strong);
      color: var(--color-text);

      &:hover {
        background: var(--color-hover-wash);
        border-color: var(--color-text-subtle);
      }
    }

    &.quiet {
      background: transparent;
      padding: 0;
      color: var(--color-text-muted);
      font-weight: 400;

      &:hover { background: transparent; color: var(--color-text); }
      &:active { scale: none; }
    }
  }

  .actions {
    display: flex;
    gap: var(--space-2);
    align-items: center;
    margin-block-start: var(--space-3);

    form { margin: 0; }
  }

  /* --- Curriculum lists: flat rows with dividers, no cards --- */

  .units, .chapters {
    list-style: none;
    padding: 0;

    > li + li { border-block-start: 1px solid var(--color-border); }
  }

  .units a {
    display: block;
    padding-block: var(--space-4);
    padding-inline: var(--space-3);
    margin-inline: calc(-1 * var(--space-3));
    border-radius: var(--radius-md);
    color: inherit;
    text-decoration: none;

    &:hover { background: var(--color-hover-wash); }

    strong { font-weight: 500; }

    p {
      font-size: var(--text-sm);
      color: var(--color-text-muted);
      margin-block-start: var(--space-1);
    }

    .meta {
      font-size: var(--text-xs);
      color: var(--color-text-subtle);
      margin-block-start: var(--space-2);
    }
  }

  .unit-code {
    font-size: var(--text-xs);
    color: var(--color-text-subtle);
    font-variant-numeric: tabular-nums;
    margin-inline-end: var(--space-1);
  }

  .chapters > li {
    padding-block: var(--space-4);

    strong { font-weight: 500; }

    .meta { margin-block-start: var(--space-1); }

    .muted { color: var(--color-text-subtle); }

    > form { margin-block-start: var(--space-3); }
  }

  /* --- Choice cards (question form and feedback) --- */

  .choice {
    position: relative;
    display: flex;
    gap: var(--space-3);
    padding: var(--space-3) var(--space-4);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-md);
    transition: border-color var(--duration-fast) var(--ease-standard),
                background-color var(--duration-fast) var(--ease-standard),
                box-shadow var(--duration-fast) var(--ease-standard),
                translate var(--duration-fast) var(--ease-standard);

    .letter {
      flex: none;
      inline-size: 1.75rem;
      block-size: 1.75rem;
      border: 1px solid var(--color-border-strong);
      border-radius: var(--radius-full);
      text-align: center;
      line-height: 1.65rem;
      font-weight: 600;
      font-size: var(--text-sm);
      color: var(--color-text-muted);
      transition: border-color var(--duration-fast) var(--ease-standard),
                  background-color var(--duration-fast) var(--ease-standard),
                  color var(--duration-fast) var(--ease-standard);
    }
  }

  .question {
    .stem {
      padding: 0;
      margin-block-end: var(--space-4);
      font-size: var(--text-lg);
      font-weight: 600;
      line-height: var(--line-height-tight);
    }

    fieldset {
      display: grid;
      gap: var(--space-2);
      padding: 0;
      border: 0;
    }

    .choice {
      cursor: pointer;

      input[type="radio"] {
        position: absolute;
        opacity: 0;
        pointer-events: none;
      }

      &:hover {
        border-color: var(--color-border-strong);
        background: var(--color-hover-wash);
        translate: 0 -1px;
        box-shadow: 0 2px 6px oklch(0% 0 0 / 0.06);
      }

      &:has(input[type="radio"]:focus-visible) {
        outline: 2px solid var(--color-accent);
        outline-offset: 2px;
      }

      &:has(input[type="radio"]:checked) {
        border-color: var(--color-accent);
        background: color-mix(in oklab, var(--color-accent) 7%, transparent);

        .letter {
          border-color: var(--color-accent);
          background: var(--color-accent);
          color: var(--color-fill-contrast);
        }
      }
    }

    input[type="submit"] { margin-block-start: var(--space-5); }
  }

  /* --- Answer feedback --- */

  @keyframes rise-in {
    from { opacity: 0; translate: 0 8px; }
    to { opacity: 1; translate: 0 0; }
  }

  @keyframes badge-pop {
    0% { scale: 0.4; }
    70% { scale: 1.2; }
    100% { scale: 1; }
  }

  @keyframes head-shake {
    0%, 100% { translate: 0 0; }
    25% { translate: -4px 0; }
    62% { translate: 3px 0; }
  }

  .feedback {
    margin-block: var(--space-5);

    &.correct { --color-verdict: var(--color-correct); }
    &.incorrect { --color-verdict: var(--color-incorrect); }

    .verdict {
      font-weight: 600;
      color: var(--color-verdict);
      animation: rise-in var(--duration-reveal) var(--ease-standard) both;
    }

    /* Reveal choreography: cards cascade in, then the correct badge
       pops and a wrong pick shakes its head */
    .choices .choice {
      animation: rise-in var(--duration-reveal) var(--ease-standard) both;

      &:nth-child(1) { animation-delay: 60ms; }
      &:nth-child(2) { animation-delay: 120ms; }
      &:nth-child(3) { animation-delay: 180ms; }
      &:nth-child(4) { animation-delay: 240ms; }

      &.right .letter {
        animation: badge-pop 350ms 550ms var(--ease-pop) both;
      }

      &.chosen:not(.right) .letter {
        animation: head-shake 300ms 550ms var(--ease-standard) both;
      }
    }

    .choices {
      list-style: none;
      margin-block: var(--space-4);
      padding: 0;
      display: grid;
      gap: var(--space-2);

      .choice {
        .text { max-width: none; }

        .tag {
          margin-inline-start: var(--space-1);
          padding: 0.125rem var(--space-2);
          border-radius: var(--radius-full);
          font-size: var(--text-xs);
          font-weight: 500;
          color: var(--color-verdict);
          background: color-mix(in oklab, var(--color-verdict) 12%, transparent);
          white-space: nowrap;
        }

        .why {
          margin-block-start: var(--space-2);
          font-size: var(--text-sm);
          color: var(--color-text-muted);

          p { margin-block-start: var(--space-1); }
        }

        &.right {
          border-color: var(--color-correct);
          background: color-mix(in oklab, var(--color-correct) 7%, transparent);

          .text { font-weight: 600; }

          .letter {
            border-color: var(--color-correct);
            background: var(--color-correct);
            color: var(--color-fill-contrast);
          }
        }

        &.chosen:not(.right) {
          border-color: var(--color-incorrect);
          background: color-mix(in oklab, var(--color-incorrect) 7%, transparent);

          .letter {
            border-color: var(--color-incorrect);
            background: var(--color-incorrect);
            color: var(--color-fill-contrast);
          }
        }
      }
    }
  }

  /* --- Sign in --- */

  .auth {
    max-width: 26rem;

    p { color: var(--color-text-muted); }

    form { margin-block-start: var(--space-5); }
  }

  .input-group {
    margin-block-end: var(--space-5);

    label {
      display: block;
      margin-block-end: var(--space-2);
      font-size: var(--text-sm);
      color: var(--color-text-muted);
    }

    input {
      inline-size: 100%;
      block-size: 3rem;
      padding-inline: var(--space-4);
      font: inherit;
      color: inherit;
      background: var(--color-surface);
      border: 1px solid var(--color-border-strong);
      border-radius: var(--radius-md);

      &::placeholder { color: var(--color-text-subtle); }
      &:focus-visible { border-color: var(--color-accent); }
    }
  }

  /* --- Dashboard --- */

  .hero-metrics {
    display: flex;
    gap: var(--space-6);
    padding: var(--space-4) var(--space-5);
    margin-block-end: var(--space-5);
    border-radius: var(--radius-md);
    background: var(--color-accent);
    color: var(--color-fill-contrast);

    .metric { display: grid; gap: var(--space-1); }

    .value {
      font-size: var(--text-2xl);
      font-weight: 600;
      line-height: var(--line-height-tight);
      font-variant-numeric: tabular-nums;

      .of {
        font-size: var(--text-sm);
        font-weight: 400;
        color: color-mix(in oklab, var(--color-fill-contrast) 78%, var(--color-accent));
      }
    }

    .label {
      font-size: var(--text-xs);
      color: color-mix(in oklab, var(--color-fill-contrast) 78%, var(--color-accent));
    }
  }

  .resume ul {
    list-style: none;
    padding: 0;

    > li + li { border-block-start: 1px solid var(--color-border); }

    a {
      display: block;
      padding-block: var(--space-3);
      padding-inline: var(--space-3);
      margin-inline: calc(-1 * var(--space-3));
      border-radius: var(--radius-md);
      color: inherit;
      text-decoration: none;

      &:hover { background: var(--color-hover-wash); }

      strong { font-weight: 500; }

      .meta {
        display: block;
        font-size: var(--text-xs);
        color: var(--color-text-subtle);
        margin-block-start: var(--space-1);
      }
    }
  }

  /* --- Attempt history --- */

  .table-container {
    border: 1px solid var(--color-border);
    border-radius: var(--radius-md);
    overflow-x: auto;
  }

  table.attempts {
    inline-size: 100%;
    border-collapse: collapse;
    font-size: var(--text-sm);

    th {
      font-size: var(--text-xs);
      font-weight: 500;
      color: var(--color-text-subtle);
      text-align: start;
      padding: var(--space-2) var(--space-4);
      border-block-end: 1px solid var(--color-border);
    }

    td { padding: var(--space-3) var(--space-4); }

    tbody tr:nth-child(even) { background: var(--color-hover-wash); }

    a {
      color: inherit;
      font-weight: 500;
      text-decoration: none;

      &:hover { text-decoration: underline; }
    }

    td .meta {
      font-size: var(--text-xs);
      color: var(--color-text-subtle);
      margin-inline-start: var(--space-2);
    }

    .when { color: var(--color-text-muted); }

    .numeric {
      text-align: end;
      font-variant-numeric: tabular-nums;
    }
  }

  /* --- Results: score as the hero metric --- */

  .score {
    display: flex;
    align-items: baseline;
    gap: var(--space-3);
    padding: var(--space-4) var(--space-5);
    border-radius: var(--radius-md);
    background: var(--color-accent);
    color: var(--color-fill-contrast);

    .value {
      font-size: var(--text-2xl);
      font-weight: 600;
      line-height: var(--line-height-tight);
      font-variant-numeric: tabular-nums;
    }

    .label {
      font-size: var(--text-sm);
      color: color-mix(in oklab, var(--color-fill-contrast) 78%, var(--color-accent));
    }
  }

  .review {
    list-style: none;
    padding: 0;
    margin-block: var(--space-6);

    > li {
      padding-block: var(--space-5);

      + li { border-block-start: 1px solid var(--color-border); }

      .stem { font-weight: 500; }

      .feedback { margin-block: var(--space-3) 0; }
    }
  }
}