/* ========================================================================
   AI Infra with OS — ACM SIGOPS ATC 2026 Tutorial
   Pure academic style: clean white background, serif headings,
   tabular schedule, minimal decoration.
   ======================================================================== */

:root {
    --ink: #1a1a1a;
    --ink-soft: #333;
    --ink-faint: #666;
    --rule: #ccc;
    --rule-soft: #e8e8e8;
    --paper: #fff;
    --paper-off: #f8f8f8;
    --accent: #0b3d2e;
    --link: #0b4f6e;
    --link-hover: #073245;
    --maxw: 1100px;
    --nav-h: 56px;
}

* { margin: 0; padding: 0; box-sizing: border-box; }

html {
    scroll-behavior: smooth;
    scroll-padding-top: calc(var(--nav-h) + 16px);
}

body {
    font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
    color: var(--ink);
    background: var(--paper);
    line-height: 1.75;
    font-size: 17px;
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
    text-rendering: optimizeLegibility;
}

/* ========================================================================
   Navigation — slim, transparent over hero
   ======================================================================== */

.navbar {
    background: rgba(255, 255, 255, 0.95);
    backdrop-filter: saturate(180%) blur(10px);
    -webkit-backdrop-filter: saturate(180%) blur(10px);
    border-bottom: 1px solid var(--rule);
    padding: 0;
    height: var(--nav-h);
    transition: box-shadow 0.25s ease;
}

.navbar.scrolled {
    box-shadow: 0 1px 0 rgba(0,0,0,0.06), 0 4px 12px rgba(0,0,0,0.06);
}

.navbar .container {
    height: 100%;
    display: flex;
    align-items: center;
}

.navbar-brand {
    font-family: 'Source Serif 4', Georgia, serif;
    font-size: 1.15rem;
    font-weight: 700;
    color: var(--ink);
    padding: 0;
    margin: 0;
}

.navbar-brand .brand-accent {
    color: var(--accent);
}

.navbar-nav { align-items: center; }

.nav-link {
    color: var(--ink-soft) !important;
    font-size: 0.95rem;
    font-weight: 500;
    padding: 0.4rem 0.85rem !important;
    transition: color 0.2s ease;
}

.nav-link:hover { color: var(--accent) !important; }

.navbar-toggler {
    border: 1px solid var(--rule);
    padding: 0.3rem 0.55rem;
}

.navbar-toggler:focus { box-shadow: none; }

/* ========================================================================
   Hero — background banner
   ======================================================================== */

.hero {
    position: relative;
    color: #fff;
    background-color: #0a121b;
    overflow: hidden;
    width: 100%;
    min-height: 900px;
    display: flex;
    align-items: center;
}

.hero::before {
    content: '';
    position: absolute;
    inset: 0;
    background-image: url('images/background.png');
    background-size: cover;
    background-position: center;
    background-repeat: no-repeat;
    z-index: 0;
}

.hero::after {
    content: '';
    position: absolute;
    inset: 0;
    background: linear-gradient(180deg, rgba(8,16,26,0.45) 0%, rgba(10,30,40,0.30) 50%, rgba(6,16,24,0.65) 100%);
    z-index: 1;
}

.hero-inner {
    position: relative;
    z-index: 2;
    max-width: 1200px;
    margin: 0 auto;
    padding: 6rem 2rem 5rem;
    width: 100%;
}

.hero h1 {
    font-family: 'Source Serif 4', Georgia, serif;
    font-size: clamp(2.5rem, 7vw, 5rem);
    font-weight: 700;
    line-height: 1.15;
    margin-bottom: 1rem;
    text-shadow: 0 2px 20px rgba(0,0,0,0.6), 0 0 40px rgba(0,0,0,0.3);
    color: #fff;
    letter-spacing: -0.02em;
}

.hero-lede {
    font-size: 1.25rem;
    line-height: 1.65;
    color: rgba(255,255,255,0.95);
    max-width: 72ch;
    margin-bottom: 2rem;
    text-shadow: 0 1px 8px rgba(0,0,0,0.4);
}

.hero-meta {
    display: flex;
    flex-wrap: wrap;
    gap: 2rem;
    font-size: 1rem;
    color: rgba(255,255,255,0.9);
}

.hero-meta-item {
    display: flex;
    flex-direction: column;
    gap: 0.15rem;
}

.hero-meta-label {
    font-size: 0.72rem;
    text-transform: uppercase;
    letter-spacing: 0.12em;
    color: rgba(255,255,255,0.65);
    font-weight: 600;
}

.hero-meta-value {
    font-weight: 600;
    text-shadow: 0 1px 6px rgba(0,0,0,0.4);
}

/* ========================================================================
   Page body
   ======================================================================== */

main {
    max-width: var(--maxw);
    margin: 0 auto;
    padding: 3rem 1.5rem 2rem;
}

section {
    margin-bottom: 3.5rem;
    scroll-margin-top: calc(var(--nav-h) + 16px);
}

.section-title {
    font-family: 'Source Serif 4', Georgia, serif;
    font-size: 1.6rem;
    font-weight: 700;
    color: var(--ink);
    margin-bottom: 1.2rem;
    padding-bottom: 0.5rem;
    border-bottom: 2px solid var(--accent);
}

.prose {
    font-size: 1.05rem;
    color: var(--ink-soft);
    line-height: 1.85;
}

.prose p { margin-bottom: 1rem; }
.prose p:last-child { margin-bottom: 0; }
.prose strong { color: var(--ink); font-weight: 600; }

.prose a {
    color: var(--link);
    text-decoration: underline;
    text-underline-offset: 2px;
}

.prose a:hover { color: var(--link-hover); }

/* ========================================================================
   Schedule — clean table
   ======================================================================== */

.schedule-note {
    font-size: 0.95rem;
    color: var(--ink-faint);
    margin-bottom: 1.2rem;
}

.schedule {
    width: 100%;
    border-collapse: collapse;
    font-size: 1rem;
}

.schedule th {
    text-align: left;
    font-size: 0.82rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.06em;
    color: var(--ink-faint);
    padding: 0.6rem 0.8rem;
    border-bottom: 2px solid var(--accent);
}

.schedule td {
    padding: 0.75rem 0.8rem;
    border-bottom: 1px solid var(--rule-soft);
    vertical-align: top;
}

.schedule tr.break-row td {
    background: var(--paper-off);
    font-style: italic;
    color: var(--ink-faint);
}

.sched-time {
    font-variant-numeric: tabular-nums;
    font-weight: 500;
    white-space: nowrap;
    color: var(--ink);
    width: 130px;
}

.sched-type {
    font-size: 0.82rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.04em;
    color: var(--accent);
    width: 90px;
}

.sched-type.talk { color: #2a4a6b; }
.sched-type.break { color: var(--ink-faint); }

.sched-title-cell {
    font-weight: 500;
    color: var(--ink);
    font-size: 1.02rem;
}

.sched-speaker {
    font-size: 0.9rem;
    color: var(--ink-faint);
    margin-top: 0.2rem;
}

/* ========================================================================
   Organizers — simple list
   ======================================================================== */

.people { margin-top: 0.3rem; }

.person {
    display: flex;
    align-items: baseline;
    gap: 0.8rem;
    padding: 0.6rem 0;
    border-bottom: 1px solid var(--rule-soft);
}

.person:last-child { border-bottom: none; }

.person-name {
    font-size: 1.05rem;
    font-weight: 600;
    color: var(--ink);
}

.person-role {
    font-size: 0.82rem;
    color: var(--ink-faint);
}

/* ========================================================================
   Footer
   ======================================================================== */

footer {
    border-top: 1px solid var(--rule);
    background: var(--paper-off);
    padding: 1.8rem 0;
    margin-top: 3rem;
}

footer .container {
    max-width: var(--maxw);
    display: flex;
    flex-wrap: wrap;
    justify-content: space-between;
    align-items: baseline;
    gap: 0.8rem;
    padding: 0 1.5rem;
}

.foot-left {
    font-size: 0.9rem;
    color: var(--ink-soft);
}

.foot-left strong {
    font-family: 'Source Serif 4', Georgia, serif;
    font-weight: 700;
    color: var(--accent);
}

.foot-right {
    font-size: 0.85rem;
    color: var(--ink-faint);
}

.foot-right a {
    color: var(--ink-soft);
    text-decoration: none;
    margin-left: 1rem;
}

.foot-right a:hover {
    color: var(--accent);
    text-decoration: underline;
}

/* ========================================================================
   TBA pill
   ======================================================================== */

.tba {
    display: inline-block;
    font-size: 0.7rem;
    font-weight: 600;
    letter-spacing: 0.06em;
    text-transform: uppercase;
    color: var(--ink-faint);
    background: var(--paper-off);
    border: 1px solid var(--rule);
    padding: 0.1rem 0.4rem;
    border-radius: 2px;
    vertical-align: middle;
    margin-left: 0.3rem;
}

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

@media (max-width: 860px) {
    .schedule { font-size: 0.92rem; }
    .sched-time { width: 110px; }
    .sched-type { width: 80px; }
    footer .container { flex-direction: column; align-items: flex-start; }
    .foot-right a { margin-left: 0; margin-right: 1rem; }
}

@media (max-width: 600px) {
    .hero-inner { padding: 4rem 1.25rem 2.5rem; }
    main { padding: 2rem 1.25rem 1.5rem; }
    .hero-meta { gap: 1.2rem; }
    .schedule th, .schedule td { padding: 0.5rem 0.5rem; }
    .sched-time { width: auto; }
    .navbar-collapse {
        background: var(--paper);
        border-top: 1px solid var(--rule);
        padding: 0.5rem 0;
        margin-top: 0.5rem;
    }
    .navbar-collapse .nav-link { padding: 0.6rem 1rem !important; }
}

@media (prefers-reduced-motion: reduce) {
    *, *::before, *::after {
        animation-duration: 0.01ms !important;
        transition-duration: 0.01ms !important;
        scroll-behavior: auto !important;
    }
}