body {
    margin: 0;
    overflow-x: clip;
}

html {
    /* Extra room below the topbar height so anchored headings clear
       the topbar's drop shadow instead of landing inside it. */
    scroll-padding-top: calc(var(--topbar-height) + 0.5rem);
    overflow-x: clip;
}

/* ---- Topbar (fixed at the top of the viewport) ---------------------- */

.topbar {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    height: var(--topbar-height);
    z-index: 100;
}

/* ---- Page grid (sidebar + main column), centered -------------------- */

.page {
    display: grid;
    grid-template-columns:
        var(--left-sidebar-width)
        minmax(0, var(--content-max-width));
    max-width: var(--layout-width);
    margin: 0 auto;
    padding-top: var(--topbar-height);
    background: var(--bg);
}

.main {
    min-width: 0;
    padding: 0 24px;
}

/* ---- Article + right sidebar grid (inside .main) -------------------- */

.article-with-toc {
    display: grid;
    grid-template-columns: minmax(0, 1fr);
    gap: 32px;
    padding: 24px 0 24px 16px;
    min-height: calc(100vh - var(--topbar-height));
}

/* No-TOC pages don't get the extra left indent; index.html etc.
   handle their own horizontal padding via .article-column below. */
.article-with-toc.no-toc {
    padding-left: 0;
}

@media (min-width: 1280px) {
    .article-with-toc {
        grid-template-columns:
            minmax(0, 1fr)
            var(--right-sidebar-width);
    }

    .article-with-toc.no-toc {
        grid-template-columns: minmax(0, 1fr);
    }

    /* No-TOC pages get extra horizontal padding so prose isn't
       hugging the wide column edge. */
    .article-with-toc.no-toc > .article-column {
        padding-left: 32px;
        padding-right: 32px;
    }
}

.article-column {
    min-width: 0;
}

.article {
    min-width: 0;
}

/* ---- Mobile: collapse to single column, sidebar slides in --------- */

@media (max-width: 1024px) {
    .page {
        grid-template-columns: minmax(0, 1fr);
    }

    .sidebar-backdrop {
        position: fixed;
        inset: var(--topbar-height) 0 0 0;
        background: rgba(0, 0, 0, 0.4);
        z-index: 80;
        opacity: 0;
        pointer-events: none;
        transition: opacity 0.2s ease;
    }

    body.sidebar-open .sidebar-backdrop {
        opacity: 1;
        pointer-events: auto;
    }

    /* Don't let the page scroll behind an open sidebar. */
    body.sidebar-open {
        overflow: hidden;
    }

    .main {
        padding: 0 16px;
    }

    .article-with-toc {
        padding: 16px 0;
    }
}

@media (max-width: 600px) {
    :root {
        --topbar-height: 48px;
    }

    .main {
        padding: 0 12px;
    }
}

/* ---- Keyboard shortcut flyout (triggered by "?") ----------------- */

.shortcut-flyout {
    position: fixed;
    inset: 0;
    z-index: 200;
    display: none;
}

.shortcut-flyout.is-open {
    display: block;
}

.shortcut-flyout-backdrop {
    position: absolute;
    inset: 0;
    background: rgba(0, 0, 0, 0.45);
}

.shortcut-flyout-panel {
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    box-sizing: border-box;
    min-width: min(320px, 90vw);
    max-width: 90vw;
    background: var(--bg);
    color: var(--text);
    border: 1px solid var(--border);
    border-radius: 8px;
    box-shadow: 0 12px 36px rgba(0, 0, 0, 0.35);
    padding: 1.2em 1.4em 1.4em;
}

.shortcut-flyout-title {
    font-size: 0.78rem;
    font-weight: 700;
    letter-spacing: 0.1em;
    text-transform: uppercase;
    color: var(--text-muted);
    margin-bottom: 0.8em;
}

.shortcut-flyout-list {
    display: grid;
    grid-template-columns: auto 1fr;
    gap: 0.55em 1.2em;
    margin: 0;
}

.shortcut-flyout-list dt {
    margin: 0;
    padding: 0;
    background: transparent;
    border: 0;
    display: inline-flex;
    align-items: center;
    gap: 4px;
    white-space: nowrap;
    font-weight: 400;
}

.shortcut-flyout-list dd {
    margin: 0;
    padding: 0;
    color: var(--text);
    align-self: center;
}

/* Pill style is shared with the search-input hint
   (.search-kbd kbd in search.css). */

/* ---- "Back to top" floating button ------------------------------- */

.back-to-top {
    position: fixed;
    right: max(20px, calc((100vw - var(--layout-width)) / 2 + 20px));
    bottom: 24px;
    z-index: 90;
    display: inline-flex;
    align-items: center;
    justify-content: center;
    width: 28px;
    height: 28px;
    padding: 0;
    border: 0;
    border-radius: 999px;
    background: var(--bg-topbar);
    color: var(--text-on-dark);
    font-size: 11px;
    cursor: pointer;
    box-shadow: 0 1px 3px rgba(0, 0, 0, 0.12);
    /* Visible state below uses opacity 0.55, muted at rest so it
       doesn't grab attention; pops on hover. */
    opacity: 0;
    pointer-events: none;
    transition:
        opacity 0.2s ease,
        background 0.15s ease,
        box-shadow 0.15s ease;
}

.back-to-top.is-visible {
    opacity: 0.55;
    pointer-events: auto;
}

/* Dark mode: --bg-topbar (#181818) blends into the page bg. Use a
   lifted-surface gray so the button stays readable. */
[data-theme="dark"] .back-to-top {
    background: #3a3a3a;
    color: #f0f0f0;
    box-shadow: 0 1px 3px rgba(0, 0, 0, 0.4);
}

[data-theme="dark"] .back-to-top.is-visible {
    opacity: 0.85;
}

/* Mobile: bump size + opacity. The 28px gap-tucked button is way
   too small/subtle for touch + small screens. */
@media (max-width: 1024px) {
    .back-to-top {
        right: 14px;
        bottom: 14px;
        width: 36px;
        height: 36px;
        font-size: 13px;
        box-shadow: 0 2px 6px rgba(0, 0, 0, 0.22);
    }

    .back-to-top.is-visible,
    [data-theme="dark"] .back-to-top.is-visible {
        opacity: 1;
    }
}

/* Wide viewports: tuck the button into the 32px gap between the
   article column and the right TOC. Button is 28px, so 2px clear
   on each side. */
@media (min-width: 1280px) {
    .back-to-top {
        right: calc(
            (100vw - var(--layout-width)) / 2
            + var(--right-sidebar-width)
            + 2px
        );
    }
}

.back-to-top.is-visible:hover {
    opacity: 1;
    box-shadow: 0 2px 8px rgba(0, 0, 0, 0.2);
}

.back-to-top:focus-visible {
    outline: 2px solid var(--accent-ring);
    outline-offset: 3px;
}