/* ============================================================
   Jiyuan Han — Academic Personal Website
   ============================================================ */

/* --- CSS Variables --- */
:root {
    --color-bg: #fafaf9;
    --color-surface: #ffffff;
    --color-text: #1c1917;
    --color-text-secondary: #57534e;
    --color-text-muted: #8c8a84;
    --color-accent: #1e40af;
    --color-accent-hover: #1e3a8a;
    --color-border: #e7e5e4;
    --color-border-light: #f0efed;
    --color-tag-bg: #eff6ff;
    --color-tag-text: #1e40af;
    --color-tag-border: #dbeafe;
    --font-serif: 'Source Serif 4', 'Charter', 'Georgia', 'Times New Roman', serif;
    --font-sans: -apple-system, BlinkMacSystemFont, 'Segoe UI', 'Inter', Roboto, 'Helvetica Neue', sans-serif;
    --font-mono: 'SF Mono', 'Fira Code', 'Fira Mono', 'Roboto Mono', monospace;
    --max-width: 780px;
    --radius: 6px;
}

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

html {
    scroll-behavior: smooth;
    scroll-padding-top: 80px;
}

body {
    font-family: var(--font-sans);
    font-size: 16px;
    line-height: 1.7;
    color: var(--color-text);
    background-color: var(--color-bg);
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
}

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

/* --- Header --- */
.header {
    padding: 60px 0 36px;
    border-bottom: 1px solid var(--color-border);
    margin-bottom: 0;
}

.header-content {
    display: flex;
    align-items: flex-start;
    justify-content: space-between;
    gap: 32px;
}

.header-text h1 {
    font-family: var(--font-serif);
    font-size: 2rem;
    font-weight: 600;
    color: var(--color-text);
    letter-spacing: -0.02em;
    line-height: 1.2;
    margin-bottom: 6px;
}

.header-text h1 .phd {
    font-weight: 400;
    color: var(--color-text-secondary);
    font-size: 0.85em;
}

.header-text .title {
    font-size: 1.1rem;
    color: var(--color-text-secondary);
    margin-bottom: 4px;
    font-weight: 400;
}

.header-text .affiliation {
    font-size: 0.95rem;
    color: var(--color-text-secondary);
    margin-bottom: 16px;
}

.header-text .affiliation a {
    color: var(--color-accent);
    text-decoration: none;
    font-weight: 500;
}

.header-text .affiliation a:hover {
    text-decoration: underline;
}

.separator {
    color: var(--color-text-muted);
    margin: 0 6px;
}

.contact-links {
    display: flex;
    flex-wrap: wrap;
    gap: 14px;
}

.contact-item {
    display: inline-flex;
    align-items: center;
    gap: 5px;
    font-size: 0.9rem;
    color: var(--color-text-secondary);
    text-decoration: none;
}

.contact-item[href]:hover {
    color: var(--color-accent);
    text-decoration: underline;
}

.contact-item svg {
    flex-shrink: 0;
    color: var(--color-text-muted);
}

.header-photo {
    flex-shrink: 0;
}

.header-photo img {
    width: 160px;
    height: 160px;
    border-radius: 50%;
    object-fit: cover;
    border: 3px solid var(--color-border-light);
    box-shadow: 0 1px 3px rgba(0,0,0,0.06);
}

/* --- Navigation --- */
.nav {
    display: flex;
    gap: 4px;
    padding: 12px 0;
    margin-bottom: 32px;
    border-bottom: 1px solid var(--color-border);
    flex-wrap: wrap;
    position: sticky;
    top: 0;
    background-color: rgba(250, 250, 249, 0.92);
    backdrop-filter: blur(8px);
    -webkit-backdrop-filter: blur(8px);
    z-index: 10;
}

.nav a {
    display: inline-block;
    padding: 6px 14px;
    font-size: 0.88rem;
    font-weight: 500;
    color: var(--color-text-secondary);
    text-decoration: none;
    border-radius: var(--radius);
    transition: background-color 0.15s ease, color 0.15s ease;
}

.nav a:hover {
    background-color: var(--color-border-light);
    color: var(--color-text);
}

/* --- Sections --- */
section {
    padding: 32px 0;
    border-bottom: 1px solid var(--color-border-light);
}

section:last-of-type {
    border-bottom: none;
}

section h2 {
    font-family: var(--font-serif);
    font-size: 1.4rem;
    font-weight: 600;
    color: var(--color-text);
    margin-bottom: 18px;
    letter-spacing: -0.01em;
    position: relative;
}

section h3 {
    font-size: 1.05rem;
    font-weight: 600;
    color: var(--color-text-secondary);
    margin: 28px 0 12px;
    text-transform: uppercase;
    letter-spacing: 0.04em;
    font-size: 0.8rem;
}

section p {
    margin-bottom: 12px;
    color: var(--color-text-secondary);
    line-height: 1.75;
}

section a {
    color: var(--color-accent);
    text-decoration: none;
}

section a:hover {
    text-decoration: underline;
}

/* --- Keywords --- */
.keywords {
    display: flex;
    flex-wrap: wrap;
    gap: 8px;
    margin-top: 20px;
}

.keywords span {
    display: inline-block;
    padding: 4px 12px;
    font-size: 0.82rem;
    font-weight: 500;
    color: var(--color-tag-text);
    background-color: var(--color-tag-bg);
    border: 1px solid var(--color-tag-border);
    border-radius: 999px;
    white-space: nowrap;
}

/* --- Publications --- */
.pubs {
    list-style: none;
    counter-reset: pub-counter;
    padding-left: 0;
}

.pub {
    position: relative;
    padding: 18px 0 18px 36px;
    border-bottom: 1px solid var(--color-border-light);
}

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

.pub::before {
    counter-increment: pub-counter;
    content: "[" counter(pub-counter) "]";
    position: absolute;
    left: 0;
    top: 18px;
    font-size: 0.85rem;
    font-weight: 600;
    color: var(--color-text-muted);
    font-family: var(--font-mono);
}

.pub-title {
    font-size: 0.98rem;
    font-weight: 600;
    line-height: 1.45;
    margin-bottom: 4px;
}

.pub-title a {
    color: var(--color-text);
    text-decoration: none;
}

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

.math-stylized {
    font-family: 'Latin Modern Math', 'Cambria Math', 'STIX Two Math', serif;
    font-style: italic;
}

.pub-authors {
    font-size: 0.9rem;
    color: var(--color-text-secondary);
    margin-bottom: 4px;
}

.pub-meta {
    font-size: 0.82rem;
    color: var(--color-text-muted);
    display: flex;
    flex-wrap: wrap;
    gap: 8px;
}

.pub-meta .pub-journal {
    font-style: italic;
    color: var(--color-text-secondary);
}

.pub-meta .pub-tag {
    font-family: var(--font-mono);
    font-size: 0.78rem;
    color: var(--color-text-muted);
    background-color: var(--color-border-light);
    padding: 1px 6px;
    border-radius: 3px;
}

.pub-links {
    margin-top: 6px;
    display: flex;
    gap: 8px;
}

.pub-link {
    font-family: var(--font-mono);
    font-size: 0.78rem;
    padding: 1px 8px;
    background-color: var(--color-tag-bg);
    color: var(--color-accent);
    border-radius: 3px;
    text-decoration: none;
    border: 1px solid var(--color-tag-border);
    transition: background-color 0.15s ease;
}

.pub-link:hover {
    background-color: var(--color-tag-border);
    text-decoration: none;
}

/* --- Talks --- */
.talks-list {
    list-style: none;
    padding-left: 0;
}

.talks-list li {
    padding: 14px 0;
    border-bottom: 1px solid var(--color-border-light);
}

.talks-list li:last-child {
    border-bottom: none;
}

.talk-title {
    font-weight: 600;
    font-size: 0.95rem;
    color: var(--color-text);
    margin-bottom: 2px;
}

.talk-venue {
    font-size: 0.88rem;
    color: var(--color-text-secondary);
}

.talk-date {
    font-size: 0.8rem;
    color: var(--color-text-muted);
}

/* --- Contact --- */
.contact-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
    gap: 20px;
    margin-top: 8px;
}

.contact-card {
    padding: 16px;
    background-color: var(--color-surface);
    border: 1px solid var(--color-border);
    border-radius: var(--radius);
}

.contact-card .contact-label {
    font-size: 0.75rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.06em;
    color: var(--color-text-muted);
    margin-bottom: 6px;
}

.contact-card a {
    font-size: 0.92rem;
    color: var(--color-accent);
    text-decoration: none;
    word-break: break-all;
}

.contact-card a:hover {
    text-decoration: underline;
}

.contact-card span {
    font-size: 0.92rem;
    color: var(--color-text-secondary);
    display: block;
}

/* --- Footer --- */
footer {
    padding: 36px 0 48px;
    text-align: center;
    font-size: 0.82rem;
    color: var(--color-text-muted);
}

footer p {
    margin-bottom: 6px;
}

.footer-links a {
    color: var(--color-text-secondary);
    text-decoration: none;
}

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

/* --- Responsive --- */
@media (max-width: 640px) {
    .header {
        padding: 36px 0 28px;
    }

    .header-content {
        flex-direction: column-reverse;
        align-items: flex-start;
        text-align: left;
    }

    .header-photo img {
        width: 120px;
        height: 120px;
    }

    .header-text h1 {
        font-size: 1.6rem;
    }

    .contact-links {
        flex-direction: column;
        gap: 8px;
    }

    .nav {
        gap: 2px;
        padding: 8px 0;
    }

    .nav a {
        padding: 6px 10px;
        font-size: 0.82rem;
    }

    section {
        padding: 24px 0;
    }

    .contact-grid {
        grid-template-columns: 1fr;
    }

    .pub {
        padding-left: 30px;
    }
}

/* --- Print --- */
@media print {
    .nav {
        display: none;
    }

    body {
        background-color: white;
        font-size: 12px;
        line-height: 1.5;
    }

    .container {
        max-width: 100%;
    }

    .header-photo img {
        width: 120px;
        height: 120px;
    }
}