:root {
    --color-bg: #ffffff;
    --color-text: #1a1a1a;
    --color-text-light: #666;
    --color-border: #e0e0e0;
    --spacing-xs: 0.5rem;
    --spacing-sm: 1rem;
    --spacing-md: 2rem;
    --spacing-lg: 4rem;
    --spacing-xl: 6rem;
}

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

html {
    scroll-behavior: smooth;
}

body {
    font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
    background-color: var(--color-bg);
    color: var(--color-text);
    line-height: 1.7;
    -webkit-font-smoothing: antialiased;
}

/* Navigation */
.nav {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    background: rgba(255, 255, 255, 0.95);
    backdrop-filter: blur(10px);
    z-index: 100;
    border-bottom: 1px solid var(--color-border);
}

.nav-content {
    max-width: 900px;
    margin: 0 auto;
    padding: var(--spacing-sm) var(--spacing-md);
    display: flex;
    gap: var(--spacing-md);
    justify-content: center;
}

.nav-link {
    color: var(--color-text-light);
    text-decoration: none;
    font-size: 0.9rem;
    font-weight: 400;
    transition: color 0.2s ease;
}

.nav-link:hover,
.nav-link.active {
    color: var(--color-text);
}

/* Hero Section */
.hero {
    min-height: 100vh;
    display: flex;
    align-items: center;
    justify-content: center;
    padding: var(--spacing-xl) var(--spacing-md);
}

.hero-content {
    max-width: 600px;
    text-align: center;
}

.profile-image {
    margin-bottom: var(--spacing-md);
}

.profile-image img {
    width: 120px;
    height: 120px;
    border-radius: 50%;
    object-fit: cover;
}

.greeting {
    font-size: 1rem;
    color: var(--color-text-light);
    font-weight: 400;
    margin-bottom: var(--spacing-xs);
}

.name {
    font-size: clamp(2.5rem, 6vw, 4rem);
    font-weight: 600;
    letter-spacing: -0.02em;
    line-height: 1.1;
    margin-bottom: var(--spacing-xs);
}

.name-kr {
    font-size: 1.2rem;
    color: var(--color-text-light);
    font-weight: 300;
    margin-bottom: var(--spacing-sm);
}

.role {
    font-size: 1rem;
    color: var(--color-text-light);
    font-weight: 400;
    margin-bottom: var(--spacing-md);
}

.divider {
    width: 40px;
    height: 1px;
    background: var(--color-text);
    margin: var(--spacing-md) auto;
}

.bio {
    font-size: 1rem;
    line-height: 1.7;
    color: var(--color-text-light);
    font-weight: 300;
}

/* Section Base */
section {
    padding: var(--spacing-xl) var(--spacing-md);
}

.section-content {
    max-width: 700px;
    margin: 0 auto;
}

.section-title {
    font-size: 1.5rem;
    font-weight: 600;
    margin-bottom: var(--spacing-lg);
    letter-spacing: -0.01em;
}

/* About Section */
.about {
    border-top: 1px solid var(--color-border);
}

.about-intro {
    font-size: 1.1rem;
    color: var(--color-text-light);
    font-weight: 300;
    line-height: 1.8;
}

/* Experience Section */
.experience {
    border-top: 1px solid var(--color-border);
}

.timeline {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-lg);
}

.timeline-item {
    display: grid;
    grid-template-columns: 140px 1fr;
    gap: var(--spacing-md);
    align-items: start;
}

.timeline-date {
    font-size: 0.85rem;
    color: var(--color-text-light);
    font-weight: 400;
}

.timeline-item h3 {
    font-size: 1rem;
    font-weight: 500;
    margin-bottom: 0.25rem;
    color: var(--color-text);
}

.timeline-item p {
    font-size: 0.9rem;
    color: var(--color-text-light);
    font-weight: 300;
}

/* Publications Section */
.publications {
    border-top: 1px solid var(--color-border);
}

.pub-section {
    margin-bottom: var(--spacing-xl);
}

.pub-section:last-child {
    margin-bottom: 0;
}

.subsection-title {
    font-size: 1rem;
    font-weight: 500;
    margin-bottom: var(--spacing-md);
    color: var(--color-text);
}

.item-list {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-md);
}

.item {
    display: grid;
    grid-template-columns: 140px 1fr;
    gap: var(--spacing-md);
    align-items: start;
}

.item-date {
    font-size: 0.85rem;
    color: var(--color-text-light);
    font-weight: 400;
}

.item-content {
    display: flex;
    flex-direction: column;
    gap: 0.25rem;
}

.item-title {
    font-size: 0.95rem;
    font-weight: 400;
    color: var(--color-text);
    line-height: 1.5;
}

.item-meta {
    font-size: 0.85rem;
    color: var(--color-text-light);
    font-weight: 300;
}

/* Contact Section */
.contact {
    border-top: 1px solid var(--color-border);
}

.contact-grid {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: var(--spacing-sm);
}

.contact-item {
    display: flex;
    justify-content: center;
    align-items: center;
    padding: var(--spacing-sm);
    text-decoration: none;
    color: var(--color-text);
    border: 1px solid var(--color-border);
    transition: border-color 0.2s ease;
}

.contact-item:hover {
    border-color: var(--color-text);
}

.contact-label {
    font-weight: 400;
    font-size: 0.9rem;
}

.contact-arrow {
    display: none;
}

/* Email tooltip */
.email-item {
    position: relative;
    cursor: default;
}

.email-tooltip {
    position: absolute;
    bottom: calc(100% + 12px);
    left: 50%;
    transform: translateX(-50%) translateY(10px);
    background: white;
    border: 1px solid var(--color-border);
    padding: var(--spacing-sm);
    opacity: 0;
    visibility: hidden;
    transition: all 0.2s ease;
    pointer-events: none;
    min-width: 200px;
    z-index: 10;
}

.email-item:hover .email-tooltip {
    opacity: 1;
    visibility: visible;
    transform: translateX(-50%) translateY(0);
}

.email-type {
    font-size: 0.7rem;
    text-transform: uppercase;
    letter-spacing: 0.05em;
    color: var(--color-text-light);
    font-weight: 500;
    margin-bottom: 0.25rem;
}

.email-type:not(:first-child) {
    margin-top: var(--spacing-sm);
}

.email-address {
    font-size: 0.85rem;
    color: var(--color-text);
    font-family: 'Courier New', monospace;
}

/* Footer */
.footer {
    padding: var(--spacing-md);
    text-align: center;
    color: var(--color-text-light);
    font-size: 0.85rem;
    border-top: 1px solid var(--color-border);
}

/* Responsive */
@media (max-width: 768px) {
    .nav-content {
        gap: var(--spacing-sm);
        font-size: 0.85rem;
    }

    .hero {
        padding: var(--spacing-lg) var(--spacing-md);
    }

    .profile-image img {
        width: 100px;
        height: 100px;
    }

    .section-title {
        font-size: 1.3rem;
    }

    .timeline-item,
    .item {
        grid-template-columns: 1fr;
        gap: var(--spacing-xs);
    }

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

    .email-tooltip {
        min-width: 180px;
        left: 0;
        right: 0;
        margin: 0 auto;
        transform: translateY(10px);
    }

    .email-item:hover .email-tooltip {
        transform: translateY(0);
    }
}

@media (prefers-color-scheme: dark) {
    :root {
        --color-bg: #0a0a0a;
        --color-text: #e0e0e0;
        --color-text-light: #999;
        --color-border: #2a2a2a;
    }

    .nav {
        background: rgba(10, 10, 10, 0.95);
    }

    .email-tooltip {
        background: #0a0a0a;
    }
}