/* ============================================================
   Layout — Textbook Structural Positioning
   ============================================================
   Only positioning, sizing, and responsive breakpoints.
   No component styling — that lives in components.css.
   All values via tokens.css variables.

   Reference: pages/learn/DESIGN-POC.html
   ============================================================ */

/* --- Reset --- */
*,
*::before,
*::after {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}

/* --- Document --- */
html {
    scroll-behavior: smooth;
}

body {
    font-family: var(--font-body);
    background: var(--bg);
    color: var(--text);
    line-height: var(--leading-body);
    font-size: var(--text-body);
}

/* --- Navbar --- */
.navbar {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    height: var(--navbar-height);
    background: var(--bg-navbar);
    border-bottom: 1px solid var(--border);
    display: flex;
    align-items: center;
    padding: 0 var(--space-6xl);
    z-index: var(--z-navbar);
}

/* --- TOC Sidebar --- */
.toc {
    position: fixed;
    left: 0;
    top: var(--navbar-height);
    bottom: 0;
    width: var(--toc-width);
    background: var(--bg-sidebar);
    border-right: 1px solid var(--border);
    padding: var(--space-4xl) 0;
    overflow-y: auto;
    z-index: var(--z-toc);
}

/* --- Content Outer --- */
.content-outer {
    margin-left: var(--toc-width);
    margin-top: var(--navbar-height);
    display: flex;
    justify-content: center;
    padding: 0 var(--content-padding);
}

/* --- Content Area --- */
.content-area {
    max-width: calc(var(--content-width) + var(--margin-gap) + var(--margin-width));
    width: 100%;
    padding: var(--content-padding) 0 var(--area-padding-bottom);
}

/* --- Page Header --- */
.page-header {
    max-width: var(--content-width);
    margin-bottom: var(--space-xs);
}

/* --- Section Row (content + margin side by side) --- */
.sec-row {
    display: flex;
    gap: var(--margin-gap);
    margin-top: var(--content-padding);
    padding-top: var(--space-3xl);
    border-top: 1px solid var(--border);
}

.sec-row:first-of-type {
    margin-top: 0;
    border-top: none;
    padding-top: 0;
}

/* --- Main Content Column --- */
.sec-main {
    width: var(--content-width);
    flex-shrink: 0;
    min-width: 0;
}

/* --- Margin Column --- */
.sec-margin {
    width: var(--margin-width);
    flex-shrink: 0;
}

/* ============================================================
   Responsive
   ============================================================ */

/* Margin column disappears below 1100px */
@media (max-width: 1100px) {
    .sec-margin {
        display: none;
    }

    .content-area {
        max-width: var(--content-width);
    }
}

/* TOC sidebar disappears below 860px */
@media (max-width: 860px) {
    .toc {
        display: none;
    }

    .content-outer {
        margin-left: 0;
        padding: 0 var(--space-6xl);
    }
}