/* Nirjan Biswas — site-wide modern stylesheet
   Preserves the original per-page background accent colors while giving
   the whole site a clean, readable, responsive layout. */

:root {
    --accent: #0f8f46;
    --accent-dark: #0a6d34;
    --link: #1f4dd8;
    --link-hover: #0a2a99;
    --text: #1b2431;
    --muted: #4a5568;
    --card-bg: rgba(255, 255, 255, 0.85);
    --card-border: rgba(15, 143, 70, 0.18);
    --card-shadow: 0 12px 32px rgba(15, 32, 60, 0.10);
    --radius: 14px;
    --max-width: 1080px;
}

* { box-sizing: border-box; }

html { scroll-behavior: smooth; }

body {
    margin: 0;
    color: var(--text);
    font-family: "Inter", "Segoe UI", "Helvetica Neue", Arial, sans-serif;
    font-size: 17px;
    line-height: 1.65;
    -webkit-font-smoothing: antialiased;
    background-color: #9fe2bf;
}

body.page-research  { background-color: #8dd1d1; }
body.page-talks     { background-color: #b8e6fe; }
body.page-teaching  { background-color: #98b9e7; }
body.page-links     { background-color: #e0ffff; }

img { max-width: 100%; height: auto; }

a {
    color: var(--link);
    text-decoration: none;
    border-bottom: 1px solid transparent;
    transition: color .15s ease, border-color .15s ease;
}
a:hover, a:focus {
    color: var(--link-hover);
    border-bottom-color: currentColor;
}

/* ---------- Top navigation ---------- */
.site-nav {
    position: sticky;
    top: 0;
    z-index: 20;
    backdrop-filter: saturate(140%) blur(8px);
    background: rgba(255, 255, 255, 0.75);
    border-bottom: 1px solid rgba(15, 32, 60, 0.08);
}
.site-nav .nav-inner {
    max-width: var(--max-width);
    margin: 0 auto;
    padding: 14px 24px;
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: 16px;
    flex-wrap: wrap;
}
.site-nav .brand {
    font-family: "JetBrains Mono", "Fira Code", "Cascadia Code", ui-monospace, monospace;
    font-weight: 700;
    font-size: 1.05rem;
    color: var(--accent-dark);
    letter-spacing: .3px;
    border-bottom: none;
}
.site-nav ul {
    list-style: none;
    margin: 0;
    padding: 0;
    display: flex;
    gap: 6px;
    flex-wrap: wrap;
}
.site-nav a.nav-link {
    display: inline-block;
    padding: 8px 14px;
    border-radius: 999px;
    font-family: "JetBrains Mono", "Fira Code", ui-monospace, monospace;
    font-weight: 600;
    color: var(--accent-dark);
    border-bottom: none;
    transition: background .15s ease, color .15s ease;
}
.site-nav a.nav-link:hover,
.site-nav a.nav-link:focus {
    background: var(--accent);
    color: #fff;
}
.site-nav a.nav-link.active {
    background: var(--accent-dark);
    color: #fff;
}

/* ---------- Container ---------- */
.container {
    max-width: var(--max-width);
    margin: 0 auto;
    padding: 32px 24px 64px;
}

/* ---------- Hero (index) ---------- */
.hero {
    display: grid;
    grid-template-columns: minmax(0, 1fr) minmax(240px, 360px);
    gap: 32px;
    align-items: start;
    background: var(--card-bg);
    border: 1px solid var(--card-border);
    border-radius: var(--radius);
    padding: 32px;
    box-shadow: var(--card-shadow);
}
.hero-text h1 {
    margin: 0 0 6px;
    font-size: clamp(2rem, 4vw + 1rem, 3.2rem);
    line-height: 1.1;
    color: #1f2a80;
    letter-spacing: -0.5px;
}
.hero-text .tagline {
    margin: 0 0 18px;
    font-size: 1.25rem;
    color: var(--accent-dark);
    font-weight: 600;
}
.hero-text p { margin: 0 0 14px; }

.hero-photo {
    position: sticky;
    top: 84px;
}
.hero-photo figure {
    margin: 0;
    background: #fff;
    padding: 10px;
    border-radius: var(--radius);
    box-shadow: 0 10px 26px rgba(15, 32, 60, 0.15);
    border: 1px solid rgba(15, 32, 60, 0.08);
    transform: rotate(-0.5deg);
    transition: transform .25s ease;
}
.hero-photo figure:hover { transform: rotate(0deg) translateY(-2px); }
.hero-photo img {
    display: block;
    width: 100%;
    height: auto;
    border-radius: 10px;
    aspect-ratio: 4 / 3;
    object-fit: cover;
    object-position: center 20%;
}
.hero-photo figcaption {
    margin-top: 10px;
    text-align: center;
    font-size: .9rem;
    color: var(--muted);
}

.cta-row {
    display: flex;
    flex-wrap: wrap;
    gap: 10px;
    margin-top: 18px;
}
.btn {
    display: inline-flex;
    align-items: center;
    gap: 8px;
    padding: 10px 18px;
    border-radius: 999px;
    font-family: "JetBrains Mono", ui-monospace, monospace;
    font-weight: 700;
    font-size: .95rem;
    border: 2px solid var(--accent-dark);
    background: var(--accent-dark);
    color: #fff !important;
    border-bottom: 2px solid var(--accent-dark);
    box-shadow: 0 4px 12px rgba(15, 143, 70, 0.25);
}
.btn:hover, .btn:focus {
    background: var(--accent);
    border-color: var(--accent);
    color: #fff !important;
    transform: translateY(-1px);
}
.btn.btn-outline {
    background: transparent;
    color: var(--accent-dark) !important;
    box-shadow: none;
}
.btn.btn-outline:hover {
    background: var(--accent-dark);
    color: #fff !important;
}

/* ---------- Cards / sections ---------- */
.card {
    background: var(--card-bg);
    border: 1px solid var(--card-border);
    border-radius: var(--radius);
    padding: 28px 32px;
    margin-top: 28px;
    box-shadow: var(--card-shadow);
}
.card h2 {
    margin: 0 0 16px;
    color: var(--accent-dark);
    font-family: "JetBrains Mono", ui-monospace, monospace;
    font-size: 1.35rem;
    letter-spacing: .3px;
}
.card ul { padding-left: 20px; margin: 0; }
.card li { margin: 6px 0; }

.link-chips {
    display: flex;
    flex-wrap: wrap;
    gap: 10px;
    margin-top: 8px;
}
.link-chips a {
    display: inline-block;
    padding: 8px 14px;
    background: #fff;
    border-radius: 999px;
    border: 1px solid var(--card-border);
    font-weight: 600;
    box-shadow: 0 2px 6px rgba(15, 32, 60, 0.05);
}
.link-chips a:hover {
    background: var(--link);
    color: #fff;
    border-color: var(--link);
}

.timeline {
    list-style: none;
    padding: 0;
    margin: 0;
    position: relative;
}
.timeline::before {
    content: "";
    position: absolute;
    left: 10px;
    top: 6px;
    bottom: 6px;
    width: 2px;
    background: linear-gradient(to bottom, var(--accent), transparent);
    border-radius: 2px;
}
.timeline li {
    position: relative;
    padding: 8px 0 8px 32px;
}
.timeline li::before {
    content: "";
    position: absolute;
    left: 4px;
    top: 16px;
    width: 12px;
    height: 12px;
    border-radius: 50%;
    background: var(--accent);
    box-shadow: 0 0 0 4px rgba(15, 143, 70, 0.15);
}
.timeline .when {
    display: inline-block;
    font-family: "JetBrains Mono", ui-monospace, monospace;
    font-weight: 700;
    color: var(--accent-dark);
    margin-right: 8px;
}

.contact-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
    gap: 14px;
}
.contact-grid .item {
    background: #fff;
    border-radius: 12px;
    padding: 14px 16px;
    border: 1px solid var(--card-border);
}
.contact-grid .label {
    font-size: .85rem;
    color: var(--muted);
    text-transform: uppercase;
    letter-spacing: .06em;
    font-weight: 700;
    margin-bottom: 4px;
}

/* ---------- Legacy content wrapper (research/talks/teaching) ---------- */
.legacy-content {
    background: var(--card-bg);
    border: 1px solid var(--card-border);
    border-radius: var(--radius);
    padding: 28px 32px;
    box-shadow: var(--card-shadow);
    margin-top: 20px;
}
.legacy-content img { border-radius: 10px; }

/* Footer */
.site-footer {
    text-align: center;
    padding: 24px 12px 40px;
    color: var(--muted);
    font-size: .9rem;
}

/* ---------- Responsive ---------- */
@media (max-width: 820px) {
    .hero {
        grid-template-columns: 1fr;
        padding: 24px;
    }
    .hero-photo {
        order: -1;
        position: static;
        max-width: 340px;
        margin: 0 auto;
    }
    .card { padding: 22px; }
}
@media (max-width: 480px) {
    body { font-size: 16px; }
    .site-nav .nav-inner { padding: 10px 16px; }
    .container { padding: 20px 14px 40px; }
    .hero-text h1 { font-size: 2rem; }
}