:root {
    --color-primary: #002060;
    --color-primary-light: #E5EDF8;
    --color-text: #333333;
    --color-text-light: #666666;
    --color-bg: #FFFFFF;
    --color-bg-alt: #F8F9FA;
    --color-border: #E0E0E0;
    --font-main: "Apple SD Gothic Neo", "Noto Sans KR", "Malgun Gothic", sans-serif;
}

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

body {
    font-family: var(--font-main);
    color: var(--color-text);
    background-color: var(--color-bg);
    line-height: 1.7;
}

main {
    max-width: 900px;
    margin: 0 auto;
    padding: 0 24px 60px;
}

/* ── 헤더 ── */

header {
    background-color: var(--color-primary);
    color: white;
    text-align: center;
    padding: 60px 24px 20px;
    margin-bottom: 40px;
}

.header-content {
    max-width: 900px;
    margin: 0 auto;
}

header h1 {
    font-size: 2.8em;
    font-weight: 700;
    margin-bottom: 8px;
    letter-spacing: -0.02em;
}

.tagline {
    font-size: 1.2em;
    opacity: 0.85;
    margin-bottom: 4px;
}

.tagline-sub {
    font-size: 1em;
    opacity: 0.7;
    margin-bottom: 24px;
}

nav {
    max-width: 900px;
    margin: 0 auto;
    padding: 16px 0;
    display: flex;
    justify-content: center;
    gap: 24px;
    flex-wrap: wrap;
}

nav a {
    color: rgba(255, 255, 255, 0.8);
    text-decoration: none;
    font-size: 0.95em;
    padding: 4px 0;
    border-bottom: 2px solid transparent;
    transition: all 0.2s;
}

nav a:hover {
    color: white;
    border-bottom-color: white;
}

.lang-btn {
    color: white !important;
    background: rgba(255, 255, 255, 0.15);
    border: 1.5px solid rgba(255, 255, 255, 0.5);
    border-radius: 4px;
    padding: 2px 12px;
    font-weight: 700;
    font-size: 0.85em;
    letter-spacing: 0.05em;
    transition: all 0.2s;
}

.lang-btn:hover {
    background: rgba(255, 255, 255, 0.3);
    border-color: white;
}

/* ── 섹션 공통 ── */

section {
    margin-bottom: 48px;
}

section h2 {
    font-size: 1.5em;
    color: var(--color-primary);
    border-bottom: 2px solid var(--color-primary);
    padding-bottom: 8px;
    margin-bottom: 20px;
}

section p {
    margin-bottom: 12px;
}

/* ── 서브섹션 ── */

h3.subsection {
    font-size: 1.1em;
    color: var(--color-primary);
    margin-top: 24px;
    margin-bottom: 12px;
    padding-left: 4px;
    border-left: 3px solid var(--color-primary);
    padding-left: 10px;
}

/* ── 타임라인 ── */

.timeline {
    position: relative;
    padding-left: 20px;
    border-left: 2px solid var(--color-primary-light);
}

.timeline-item {
    position: relative;
    padding: 0 0 24px 20px;
}

.timeline-item::before {
    content: "";
    position: absolute;
    left: -8px;
    top: 6px;
    width: 12px;
    height: 12px;
    background: var(--color-primary);
    border-radius: 50%;
    border: 2px solid white;
}

.timeline-date {
    font-size: 0.85em;
    color: var(--color-primary);
    font-weight: 600;
    margin-bottom: 2px;
}

.timeline-content h3 {
    font-size: 1.1em;
    margin-bottom: 4px;
}

.timeline-content p {
    color: var(--color-text-light);
    font-size: 0.95em;
    margin-bottom: 0;
}

/* ── 논문/목록 ── */

.pub-list {
    list-style: none;
    padding: 0;
}

.pub-list li {
    padding: 10px 0;
    border-bottom: 1px solid var(--color-border);
    font-size: 0.95em;
    line-height: 1.7;
}

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

.pub-list.numbered {
    list-style: decimal;
    padding-left: 24px;
}

.pub-list.numbered li {
    padding-left: 4px;
}

.meta {
    font-size: 0.85em;
    color: var(--color-text-light);
}

/* ── 프로젝트 카드 ── */

.project-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(260px, 1fr));
    gap: 20px;
}

.project-card {
    border: 1px solid var(--color-border);
    border-radius: 8px;
    padding: 20px;
    transition: box-shadow 0.2s;
}

.project-card:hover {
    box-shadow: 0 2px 12px rgba(0, 0, 0, 0.08);
}

.project-tag {
    display: inline-block;
    background: var(--color-primary-light);
    color: var(--color-primary);
    font-size: 0.8em;
    font-weight: 600;
    padding: 2px 10px;
    border-radius: 12px;
    margin-bottom: 8px;
}

.project-card h3 {
    font-size: 1.05em;
    margin-bottom: 8px;
}

.project-card p {
    font-size: 0.9em;
    color: var(--color-text-light);
    margin-bottom: 0;
}

.project-card a {
    color: var(--color-primary);
    text-decoration: none;
}

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

/* ── 연락처 ── */

.contact-links {
    display: flex;
    flex-wrap: wrap;
    gap: 16px;
}

.contact-item {
    display: flex;
    align-items: center;
    gap: 8px;
    text-decoration: none;
    color: var(--color-text);
    padding: 12px 20px;
    border: 1px solid var(--color-border);
    border-radius: 8px;
    transition: all 0.2s;
}

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

.contact-icon {
    font-size: 1.3em;
}

/* ── 푸터 ── */

footer {
    text-align: center;
    padding: 32px 24px;
    border-top: 1px solid var(--color-border);
    color: var(--color-text-light);
    font-size: 0.85em;
}

footer p {
    margin-bottom: 4px;
}

/* ── 반응형 ── */

@media (max-width: 600px) {
    header {
        padding: 40px 16px 16px;
    }

    header h1 {
        font-size: 2em;
    }

    .tagline {
        font-size: 1em;
    }

    nav {
        gap: 12px;
    }

    nav a {
        font-size: 0.85em;
    }

    main {
        padding: 0 16px 40px;
    }

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

    .contact-links {
        flex-direction: column;
    }
}