/* ============================================================
   engineering.html — mobile density
   Loaded last. Everything below 900px only; desktop untouched.
   Pairs with js/engineering-mobile.js.

   The JS never moves existing nodes — it adds a class and inserts
   one <button> sibling. Above the breakpoint those buttons are
   display:none and nothing is collapsed, so desktop is byte-for-
   byte the layout it is today.
   ============================================================ */

/* Desktop: the injected controls do not exist visually. */
.eng-toggle,
.eng-chip-more { display: none; }

/* 900px, not 760: this has to cover the whole range the deck runs in.
   At 768 the bullets stayed expanded and a system card measured 1200px
   against 952px of room — too tall to pin without stranding its bottom. */
@media (max-width: 900px) {

  /* ---------- the toggle ---------- */
  .eng-toggle {
    display: flex;
    align-items: center;
    gap: 0.7rem;
    width: 100%;
    min-height: 44px;                       /* tap target */
    padding: 0.7rem 0;
    margin: 0.35rem 0 0;
    background: none;
    border: 0;
    /* token, not hardcoded white: this hairline separates all 19 collapsible
       rows and disappeared entirely in light mode. */
    border-top: var(--border-hair, 1px solid rgba(255, 255, 255, 0.06));
    color: inherit;
    font: inherit;
    text-align: left;
    cursor: pointer;
    -webkit-tap-highlight-color: transparent;
  }
  .eng-toggle:focus-visible {
    outline: 2px solid var(--accent, #0055FF);
    outline-offset: 3px;
  }
  .eng-toggle__label {
    flex: 1;
    font-family: var(--font-mono, monospace);
    font-size: 0.72rem;
    letter-spacing: 0.13em;
    text-transform: uppercase;
    color: var(--text-dim, #A1A1A6);
  }
  .eng-toggle__hint {
    font-family: var(--font-mono, monospace);
    font-size: 0.66rem;
    letter-spacing: 0.06em;
    color: var(--text-muted, #545456);
  }
  .eng-toggle__chev {
    width: 0.45rem;
    height: 0.45rem;
    border-right: 1.5px solid var(--text-muted, #545456);
    border-bottom: 1.5px solid var(--text-muted, #545456);
    transform: rotate(45deg) translateY(-2px);
    transition: transform 0.2s ease;
    flex: 0 0 auto;
  }
  .eng-toggle[aria-expanded="true"] .eng-toggle__chev { transform: rotate(225deg) translateY(-2px); }
  .eng-toggle[aria-expanded="true"] .eng-toggle__label { color: var(--text, #EDEDED); }

  /* ---------- what collapses ---------- */
  .eng-collapse { display: none; }
  .eng-collapse.is-open { display: revert; }

  /* the original inline label is replaced by the toggle */
  .eng-label-dupe { display: none; }

  /* ---------- 1. systems ---------- */
  .eng-sys { margin-bottom: 2rem; }
  .eng-sys__title { margin-bottom: 0.45rem; }

  /* meta: five stacked rows -> two dense columns */
  .eng-sys__meta {
    display: grid;
    grid-template-columns: auto 1fr;
    gap: 0.25rem 0.85rem;
    margin: 0;
  }
  .eng-sys__meta dt {
    font-size: 0.62rem;
    letter-spacing: 0.1em;
    text-transform: uppercase;
    opacity: 0.5;
    margin: 0;
  }
  .eng-sys__meta dd { margin: 0; font-size: 0.8rem; line-height: 1.35; }

  .eng-sys__list { margin-top: 0.5rem; padding-left: 1.05rem; }
  .eng-sys__list li + li { margin-top: 0.55rem; }
  .eng-sys__stack { margin-top: 0.75rem; }

  /* ---------- 2. capped chips ---------- */
  .eng-sys__stack .is-extra { display: none; }
  .eng-sys__stack.is-open .is-extra { display: revert; }
  .eng-chip-more { display: inline-block; list-style: none; }
  .eng-chip-more button {
    font-family: var(--font-mono, monospace);
    font-size: 0.66rem;
    letter-spacing: 0.05em;
    color: var(--accent, #0055FF);
    background: none;
    border: 1px dashed rgba(0, 85, 255, 0.45);
    padding: 0.25rem 0.55rem;
    cursor: pointer;
    min-height: 30px;
  }
  .eng-chip-more button:focus-visible {
    outline: 2px solid var(--accent, #0055FF);
    outline-offset: 2px;
  }

  /* ---------- 3. constraints ---------- */
  .eng-clause { margin-bottom: 1.1rem; }
  .eng-clause__rule { margin-bottom: 0; }
  .eng-clause .eng-toggle { margin-top: 0.2rem; }

  /* ---------- 4. stack, by layer ---------- */
  .eng-layer { margin-bottom: 0; }
  .eng-layer .eng-toggle { margin: 0; }
  .eng-layer .eng-toggle__label {
    font-size: 0.78rem;
    letter-spacing: 0.06em;
    text-transform: none;
    color: var(--text, #EDEDED);
  }
  .eng-layer__items { padding-bottom: 0.7rem; }

  /* ---------- 5. container chrome ----------
     The base layout gives each block generous padding for desktop
     reading. Collapsed on a phone that padding is most of the page,
     so it is reduced here only. */
  .eng-layer  { padding-top: 0.3rem; padding-bottom: 0.3rem; row-gap: 0; }
  .eng-clause { padding-top: 0.6rem; padding-bottom: 0.6rem; margin-bottom: 0.5rem; row-gap: 0.5rem; }
  .eng-sys    { padding-bottom: 1.25rem; margin-bottom: 1.25rem; row-gap: 1rem; }

  /* ---------- 6. section rhythm ---------- */
  .eng-sec { padding-top: clamp(3rem, 2rem + 5vw, 5rem); }
  .eng-sec__head { margin-bottom: 0.9rem; }
  .eng-sec__intro { margin-bottom: 1.35rem; }
}

@media (prefers-reduced-motion: reduce) {
  .eng-toggle__chev { transition: none; }
}