/* =========================================================
   Partho K. Paul — shared design system
   Used by index.html and teaching/index.html
   One accent color, two surface colors, one type family.
   ========================================================= */

:root {
    --bg: #ffffff;
    --bg-alt: #f5f5f7;
    --text: #1d1d1f;
    --text-2: #6e6e73;
    --text-3: #6e6e73; /* AA contrast on white and #f5f5f7 */
    --line: #d2d2d7;
    --line-soft: #e8e8ed;
    --accent: #0066cc;
    --accent-hover: #0077ed;
    --radius: 18px;
    --container: 1024px;
    --font: -apple-system, BlinkMacSystemFont, "SF Pro Text", "Inter", "Helvetica Neue", Helvetica, Arial, sans-serif;
    --font-display: -apple-system, BlinkMacSystemFont, "SF Pro Display", "Inter", "Helvetica Neue", Helvetica, Arial, sans-serif;
}

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

html { scroll-behavior: smooth; scroll-padding-top: 64px; -webkit-text-size-adjust: 100%; }

body {
    font-family: var(--font);
    font-size: 17px;
    line-height: 1.47;
    letter-spacing: -0.022em;
    color: var(--text);
    background: var(--bg);
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
}

img { max-width: 100%; height: auto; display: block; }
a { color: var(--accent); text-decoration: none; }
a:hover { text-decoration: underline; text-underline-offset: 3px; }
:focus-visible { outline: 2px solid var(--accent); outline-offset: 3px; border-radius: 4px; }
ul { list-style: none; }

.container { width: min(var(--container), 100% - 44px); margin: 0 auto; }
.container.narrow { --container: 820px; }

/* ---------- Type ---------- */
h1, h2, h3 { font-family: var(--font-display); font-weight: 600; color: var(--text); }

.eyebrow {
    font-size: 14px;
    font-weight: 600;
    letter-spacing: -0.01em;
    color: var(--text-2);
    margin-bottom: 10px;
}

.section-title {
    font-size: clamp(34px, 5vw, 48px);
    line-height: 1.08;
    letter-spacing: -0.03em;
}

.section-intro {
    font-size: 19px;
    line-height: 1.42;
    color: var(--text-2);
    max-width: 680px;
    margin-top: 16px;
}

.section-head { margin-bottom: 48px; }

/* ---------- Buttons & links ---------- */
.btn {
    display: inline-block;
    padding: 11px 22px;
    border-radius: 980px;
    font-size: 17px;
    font-weight: 400;
    line-height: 1.2;
    text-decoration: none;
    border: 0;
    cursor: pointer;
    transition: background-color .2s ease;
}
.btn:hover { text-decoration: none; }
.btn-primary { background: var(--accent); color: #fff; }
.btn-primary:hover { background: var(--accent-hover); }

.btn-secondary { background: var(--bg); color: var(--accent); box-shadow: inset 0 0 0 1px var(--line); }
.btn-secondary:hover { box-shadow: inset 0 0 0 1px var(--accent); }

.link-arrow { font-size: 17px; }

/* Skip link */
.skip { position: absolute; left: 16px; top: -100px; background: var(--bg); padding: 10px 14px; z-index: 200; border-radius: 8px; }
.skip:focus { top: 10px; }

/* Touch vs. mouse: phones get "Text" first, desktops get "Email" first */
.only-fine { display: none !important; }
@media (hover: hover) and (pointer: fine) {
    .only-touch { display: none !important; }
    .only-fine { display: inline-block !important; }
}
.link-arrow::after { content: " ›"; }

/* ---------- Announcement ---------- */
.announcement-banner {
    display: flex;
    flex-wrap: wrap;
    justify-content: center;
    gap: 2px 10px;
    padding: 12px 22px;
    background: var(--bg-alt);
    color: var(--text);
    font-size: 14px;
    text-align: center;
}
.announcement-banner a { white-space: nowrap; display: inline-block; padding: 6px 6px; margin: -6px -6px; }

/* ---------- Navigation ---------- */
.navbar {
    position: sticky;
    top: 0;
    z-index: 100;
    background: rgba(255, 255, 255, 0.8);
    backdrop-filter: saturate(180%) blur(20px);
    -webkit-backdrop-filter: saturate(180%) blur(20px);
    border-bottom: 1px solid transparent;
    transition: border-color .2s ease;
}
.navbar.scrolled { border-bottom-color: var(--line-soft); }

.nav-container {
    width: min(var(--container), 100% - 44px);
    height: 52px;
    margin: 0 auto;
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: 24px;
}
.nav-logo { font-family: var(--font-display); font-size: 17px; font-weight: 600; letter-spacing: -0.02em; color: var(--text); white-space: nowrap; }
.nav-logo:hover { text-decoration: none; }
.nav-links { display: flex; align-items: center; gap: 28px; }
.nav-link { display: inline-block; padding: 12px 0; font-size: 13px; color: var(--text); opacity: .8; letter-spacing: -0.01em; transition: opacity .2s; }
.nav-link:hover, .nav-link.active { opacity: 1; text-decoration: none; }
.nav-link.nav-resume { color: var(--accent); opacity: 1; }

/* ---------- Sections ---------- */
.section { padding: 112px 0; }
.section-alt { background: var(--bg-alt); }

/* ---------- Hero ---------- */
.hero { padding: 72px 0 112px; }
.hero-grid {
    display: grid;
    grid-template-columns: 1.15fr 0.85fr;
    gap: 64px;
    align-items: center;
}
.hero-title {
    font-size: clamp(48px, 7.5vw, 80px);
    line-height: 1.02;
    letter-spacing: -0.035em;
    font-weight: 700;
}
.hero-subtitle {
    font-family: var(--font-display);
    font-size: clamp(24px, 3vw, 32px);
    line-height: 1.15;
    letter-spacing: -0.02em;
    font-weight: 600;
    color: var(--text-2);
    margin-top: 8px;
}
.hero-description {
    font-size: 21px;
    line-height: 1.38;
    color: var(--text);
    margin-top: 28px;
    max-width: 540px;
}
.hero-meta { margin-top: 24px; color: var(--text-2); font-size: 15px; }
.hero-meta li { padding: 3px 0; }
.hero-actions { display: flex; align-items: center; gap: 28px; margin-top: 36px; flex-wrap: wrap; }

.hero-image img {
    width: 100%;
    height: auto;
    aspect-ratio: 4 / 5;
    object-fit: cover;
    border-radius: 28px;
    background: var(--bg-alt);
}

/* ---------- Research (segmented control + panes) ---------- */
.segmented-wrap { overflow-x: auto; scrollbar-width: none; margin-bottom: 32px; }
.segmented-wrap::-webkit-scrollbar { display: none; }
.segmented {
    display: inline-flex;
    gap: 2px;
    padding: 3px;
    background: #e8e8ed;
    border-radius: 980px;
    white-space: nowrap;
}
.tab-item {
    font: inherit;
    font-size: 14px;
    letter-spacing: -0.01em;
    color: var(--text);
    background: transparent;
    border: 0;
    padding: 8px 18px;
    border-radius: 980px;
    cursor: pointer;
    transition: background-color .2s, box-shadow .2s;
}
@media (hover: hover) {
    .tab-item:hover { background: rgba(255,255,255,.5); }
}
.tab-item.active {
    background: #fff;
    box-shadow: 0 1px 3px rgba(0,0,0,.08), 0 1px 1px rgba(0,0,0,.04);
    font-weight: 500;
}

.research-pane {
    display: none;
    background: var(--bg);
    border-radius: var(--radius);
    padding: 56px;
}
.research-pane.active { display: block; animation: fade .35s ease; }
@keyframes fade { from { opacity: 0; } to { opacity: 1; } }

.research-pane h3 {
    font-size: 32px;
    line-height: 1.12;
    letter-spacing: -0.025em;
    max-width: 720px;
}
.research-pane > p {
    margin-top: 20px;
    font-size: 17px;
    line-height: 1.6;
    color: var(--text-2);
    max-width: 720px;
}
.pane-figure { margin: 40px 0; }
.pane-figure img { margin: 0 auto; max-height: 420px; width: auto; height: auto; }
.pane-figure a { display: block; }

.research-illo { max-width: 880px; margin: 40px auto 48px; }
.research-illo img { display: block; width: 100%; height: auto; border-radius: var(--radius); }

.highlights {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(240px, 1fr));
    gap: 0 32px;
    border-top: 1px solid var(--line-soft);
    margin-top: 32px;
}
.highlights li {
    padding: 16px 0;
    font-size: 15px;
    color: var(--text);
    border-bottom: 1px solid var(--line-soft);
}

/* ---------- Expertise ---------- */
.skill-grid {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 20px;
}
.skill-card {
    background: var(--bg-alt);
    border-radius: var(--radius);
    padding: 32px 28px;
}
.skill-card h3 { font-size: 21px; letter-spacing: -0.02em; margin-bottom: 16px; }
.skill-card li {
    font-size: 15px;
    color: var(--text-2);
    padding: 10px 0;
    border-top: 1px solid var(--line-soft);
}

/* ---------- Publications & awards ---------- */
.pub-list { border-top: 1px solid var(--line); }
.pub {
    display: grid;
    grid-template-columns: 96px 1fr;
    gap: 24px;
    padding: 28px 0;
    border-bottom: 1px solid var(--line);
}
.pub-status { font-size: 13px; color: var(--text-3); padding-top: 4px; }
.pub-title { font-size: 19px; line-height: 1.3; letter-spacing: -0.02em; font-weight: 600; }
.pub-authors { font-size: 15px; color: var(--text-2); margin-top: 8px; }
.pub-authors strong { color: var(--text); font-weight: 600; }
.pub-journal { font-size: 14px; color: var(--text-3); margin-top: 2px; font-style: italic; }

.subhead { font-size: 24px; letter-spacing: -0.02em; margin: 72px 0 16px; }
.award-list { border-top: 1px solid var(--line); }
.award-list li {
    display: flex;
    justify-content: space-between;
    gap: 24px;
    padding: 16px 0;
    font-size: 15px;
    border-bottom: 1px solid var(--line);
}
.award-list li span { color: var(--text-3); white-space: nowrap; }

/* ---------- Teaching teaser ---------- */
.teaser { text-align: center; }
.teaser .section-intro { margin-left: auto; margin-right: auto; }
.teaser-actions { display: flex; justify-content: center; align-items: center; gap: 28px; margin-top: 32px; flex-wrap: wrap; }

/* ---------- Contact ---------- */
.contact-grid {
    display: grid;
    grid-template-columns: 1.3fr 1fr;
    gap: 64px;
    align-items: end;
}
.contact-list { margin-top: 36px; border-top: 1px solid var(--line); max-width: 520px; }
.contact-list li {
    display: flex;
    justify-content: space-between;
    gap: 16px;
    padding: 16px 0;
    border-bottom: 1px solid var(--line);
    font-size: 17px;
}
.contact-list span { color: var(--text-2); }
.cv-card {
    background: var(--bg);
    border-radius: var(--radius);
    padding: 40px;
}
.cv-card h3 { font-size: 24px; letter-spacing: -0.02em; }
.cv-card p { color: var(--text-2); margin: 10px 0 24px; font-size: 15px; }

/* ---------- Footer ---------- */
.site-footer { background: var(--bg-alt); border-top: 1px solid var(--line); }
.site-footer .container {
    display: flex;
    justify-content: space-between;
    gap: 16px;
    align-items: center;
    padding: 10px 0 18px;
    font-size: 12px;
    color: var(--text-3);
}
.site-footer nav { display: flex; flex-wrap: wrap; gap: 0 20px; }
.site-footer a { color: var(--text-2); display: inline-block; padding: 10px 0; }

/* ---------- Responsive ---------- */
@media (max-width: 900px) {
    .hero-grid { grid-template-columns: 1fr; gap: 48px; }
    .hero-image { order: -1; max-width: 360px; }
    .skill-grid { grid-template-columns: 1fr; }
    .contact-grid { grid-template-columns: 1fr; gap: 40px; }
    .research-pane { padding: 36px 28px; }
}

@media (max-width: 640px) {
    body { font-size: 16px; }
    .section { padding: 72px 0; }
    .hero { padding: 48px 0 72px; }
    .hero-description, .section-intro { font-size: 17px; }
    .nav-container { gap: 16px; }
    .nav-links { gap: 18px; overflow-x: auto; scrollbar-width: none; }
    .nav-links::-webkit-scrollbar { display: none; }
    .nav-link { white-space: nowrap; }
    .nav-hide-sm { display: none; }
    .hero-image { order: 0; max-width: 220px; }
    .tab-item { min-height: 44px; }
    .segmented-wrap {
        -webkit-mask-image: linear-gradient(to right, #000 85%, transparent);
        mask-image: linear-gradient(to right, #000 85%, transparent);
    }
    .segmented-wrap.at-end { -webkit-mask-image: none; mask-image: none; }
    .research-illo { margin: 32px 0 36px; }
    .research-pane { padding: 28px 20px; }
    .research-pane h3 { font-size: 24px; }
    .pub { grid-template-columns: 1fr; gap: 6px; }
    .award-list li { flex-direction: column; gap: 2px; }
    .contact-list li { flex-direction: column; gap: 2px; }
    .cv-card { padding: 28px 24px; }
    .site-footer .container { flex-direction: column; align-items: flex-start; gap: 4px; padding-top: 16px; }
    .site-footer p { padding-top: 6px; }
}

@media (prefers-reduced-motion: reduce) {
    html { scroll-behavior: auto; }
    .research-pane.active { animation: none; }
}