/* General book styles shared across chapters.
   (Appendix F's timeline rail lives separately in timeline.css.)
   Colours come from mdBook theme variables so these work in light, rust, coal,
   navy, and ayu without per-theme overrides. */

/* ---------------------------------------------------------------------------
   Chapter subtitle — the descriptive half of a title dropped onto its own line
   below the H1, so a long heading (e.g. "Milestone M1 — The Expression
   Evaluator") no longer has to fit one line. The short identifier stays in the
   H1; the phrase sits under it, quieter and smaller. The full title still shows
   in the sidebar via SUMMARY.md.
   --------------------------------------------------------------------------- */

.chapter-subtitle {
    margin: -0.5rem 0 1.6rem;         /* tuck it up close under the H1 */
    font-size: 2.1rem;
    font-weight: 400;
    line-height: 1.2;
    opacity: 0.75;                    /* secondary to the title, theme-aware via inherited colour */
}

/* ---------------------------------------------------------------------------
   Concept checks — the collapsible question/answer blocks closing each chapter
   (plan §9.5). Without spacing they read as one undifferentiated block, so each
   gets breathing room and a visible panel when opened.
   --------------------------------------------------------------------------- */

details {
    margin: 1.4rem 0;
    padding: 0.7rem 1rem;
    border: 1px solid var(--quote-border);
    border-left-width: 3px;
    border-radius: 4px;
    background: var(--quote-bg);
}

/* the question itself: clearly clickable, readable closed or open */
details > summary {
    cursor: pointer;
    font-weight: 600;
    /* leave room for the disclosure triangle without it crowding the text */
    padding-left: 0.2rem;
}

details > summary:hover {
    color: var(--links);
}

/* when open, separate the question from its answer */
details[open] > summary {
    margin-bottom: 0.7rem;
    padding-bottom: 0.6rem;
    border-bottom: 1px solid var(--quote-border);
}

/* no trailing gap inside the panel */
details > :last-child {
    margin-bottom: 0;
}

/* consecutive checks need a clear gap, not just their own margins collapsing */
details + details {
    margin-top: 1.6rem;
}

/* ---------------------------------------------------------------------------
   Figures — historical photographs and diagrams. Captions carry the credit and
   licence line, which for third-party images is a condition of use rather than
   decoration: keep it legible, and never hide it at small widths.
   --------------------------------------------------------------------------- */

figure {
    margin: 1.8rem 0;
}

figure img {
    display: block;
    max-width: 100%;
    height: auto;
    margin: 0 auto;
    border-radius: 3px;
}

figure figcaption {
    margin-top: 0.7rem;
    font-size: 0.9em;
    line-height: 1.45;
    color: var(--sidebar-fg);
    text-align: center;
}

/* the attribution half of a caption sits below the descriptive half */
figure figcaption .credit {
    display: block;
    margin-top: 0.35rem;
    font-size: 0.92em;
    opacity: 0.85;
}

/* ---------------------------------------------------------------------------
   Scope-figure binding colours. A fixed categorical palette of three distinct
   hues shared by the "scope of a binding" SVG (binding/lexical-scope.md) and the
   prose that walks it, so a coloured binder in the text points at the bar of the
   same colour in the figure. Held identical across every theme on purpose — the
   figure's fill values are literal, so these must match them, not the theme —
   which is why they are hardcoded rather than drawn from a theme variable.
   --------------------------------------------------------------------------- */

.sc-blue   { color: #2563EB; }
.sc-green  { color: #047857; }
.sc-orange { color: #C2410C; }