/* PhysEngine Design System */
:root {
    --black: #fff;
    --white: #1a1a2e;
    --glass: rgba(26, 26, 46, 0.1);
    --glass-border: rgba(26, 26, 46, 0.35);
    --overlay: rgba(255, 255, 255, 0.5);
    --font-display: 'Segoe UI', 'Helvetica Neue', Arial, sans-serif;
    --font-body: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'Helvetica Neue', Arial, sans-serif;
}

*, ::before, ::after { margin: 0; padding: 0; box-sizing: border-box; }
html { scroll-behavior: smooth; }
body { font-family: var(--font-body); background: var(--black); color: var(--white); line-height: 1.6; }
a { text-decoration: none; color: inherit; }
ul { list-style: none; }

/* Navigation */
.navbar { position: fixed; top: 0; left: 0; width: 100%; display: flex; justify-content: space-between; align-items: center; padding: 1.2rem 3rem; z-index: 1000; background: rgba(255,255,255,0.9); }
.nav-logo { font-family: var(--font-display); font-size: 1.2rem; font-weight: 700; letter-spacing: 1px; color: var(--white); }
.nav-links { display: flex; gap: 3rem; }
.nav-links a { font-family: var(--font-display); font-size: 0.81rem; font-weight: 700; text-transform: uppercase; letter-spacing: 1.17px; color: var(--white); transition: opacity 0.3s; }
.nav-links a:hover { opacity: 0.7; }

/* Buttons */
.hero-buttons { display: flex; gap: 1rem; justify-content: center; }
.btn { padding: 1rem 2.5rem; font-size: 1rem; font-weight: 600; border-radius: 4px; transition: all 0.3s; cursor: pointer; }
.btn-primary { background: var(--white); color: var(--black); border: 2px solid var(--white); }
.btn-primary:hover { background: rgba(26, 26, 46, 0.9); transform: translateY(-2px); }
.btn-secondary { background: transparent; color: var(--white); border: 2px solid rgba(26, 26, 46, 0.7); }
.btn-secondary:hover { border-color: var(--white); background: rgba(26, 26, 46, 0.15); transform: translateY(-2px); }

.ghost-btn { display: inline-block; padding: 18px; font-family: var(--font-display); font-size: 0.81rem; font-weight: 700; text-transform: uppercase; letter-spacing: 1.17px; color: var(--white); background: var(--glass); border: 1px solid #fff; border-radius: 32px; transition: background 0.3s, border-color 0.3s; cursor: pointer; }
.ghost-btn:hover { background: rgba(26, 26, 46, 0.2); border-color: #fff; }

/* Typography */
.display-hero { font-family: var(--font-display); font-size: 3rem; font-weight: 700; letter-spacing: 0.96px; line-height: 1; margin-bottom: 1.5rem; color: var(--white); }
.body-text { font-family: var(--font-body); font-size: 1rem; line-height: 1.6; margin-bottom: 2rem; text-transform: uppercase; color: var(--white); }
.label { font-family: var(--font-display); font-size: 0.63rem; font-weight: 700; text-transform: uppercase; letter-spacing: 1px; line-height: 0.94; margin-bottom: 1rem; color: var(--white); }
.caption-bold { font-family: var(--font-display); font-size: 0.81rem; font-weight: 700; text-transform: uppercase; letter-spacing: 1.17px; line-height: 0.94; color: var(--white); }
.caption { font-family: var(--font-body); font-size: 0.75rem; font-weight: 400; text-transform: uppercase; color: var(--white); }
.back-link { display: inline-block; margin-bottom: 3rem; font-family: var(--font-display); font-size: 0.75rem; font-weight: 700; text-transform: uppercase; letter-spacing: 1px; opacity: 0.7; transition: opacity 0.3s; color: var(--white); }
.back-link:hover { opacity: 1; }

/* Section */
.section { position: relative; min-height: 100vh; display: flex; align-items: center; background-size: cover; background-position: center; background: var(--black); }
.section::before { content: ''; position: absolute; inset: 0; background: var(--overlay); z-index: 1; }
.section-content { position: relative; z-index: 2; padding: 4rem; max-width: 800px; }
.section-content.centered { max-width: 900px; margin: 0 auto; text-align: center; }
.section-content.centered .display-hero { font-size: 2.5rem; }

/* Hero */
.hero { background: url('assets/Background.png') fixed center/cover; }
.hero::before { background: transparent; }
.hero-content { position: relative; z-index: 2; padding: 4rem; text-align: left; }
.hero .display-hero { font-size: 4rem; margin-bottom: 1rem; color: var(--white); }
.hero .subtitle { font-family: var(--font-body); font-size: 1.2rem; font-weight: 400; text-transform: uppercase; margin-bottom: 3rem; letter-spacing: 0.5px; color: var(--white); opacity: 0.8; }

/* Card Section */
.card-section { position: relative; min-height: 100vh; display: flex; align-items: center; background: url('assets/Background.png') fixed center/cover; }
.card-section::before { background: transparent; }
.card-content { position: relative; z-index: 2; padding: 4rem; max-width: 600px; color: var(--white); }
.card-content.right { margin-left: auto; margin-right: 4rem; color: #fff; }
.card-content.right .display-hero,
.card-content.right .label,
.card-content.right .body-text { color: #fff; }

/* Case Cards */
.cases-page { position: relative; min-height: 100vh; background: url('assets/Background.png') fixed center/cover; }
.cases-page::before { content: ''; position: absolute; inset: 0; background: rgba(255, 255, 255, 0.7); }
.cases-grid { display: grid; grid-template-columns: repeat(2, 1fr); gap: 2rem; padding: 8rem 4rem; position: relative; z-index: 1; }
.case-card { position: relative; min-height: 400px; display: flex; align-items: center; background-size: cover; background-position: center; cursor: pointer; overflow: hidden; }
.case-card::before { content: ''; position: absolute; inset: 0; background: var(--overlay); z-index: 1; }
.case-card:hover::before { background: rgba(255,255,255,0.3); }
.case-card-content { position: relative; z-index: 2; padding: 3rem; }
.case-card .card-label { font-family: var(--font-display); font-size: 0.63rem; font-weight: 700; text-transform: uppercase; letter-spacing: 1px; margin-bottom: 1rem; color: var(--white); }
.case-card .card-title { font-family: var(--font-display); font-size: 2rem; font-weight: 700; text-transform: uppercase; letter-spacing: 0.96px; margin-bottom: 1rem; color: var(--white); }
.case-card .card-desc { font-size: 0.95rem; text-transform: uppercase; margin-bottom: 2rem; color: var(--white); }
#case-ship-card { background: linear-gradient(135deg, #1a2a4a, #0d1520); }
#case-platform-card { background: linear-gradient(135deg, #1a3a3a, #0d2020); }
#case-tunnel-card { background: linear-gradient(135deg, #2a3a5a, #152535); }
#case-stent-card { background: linear-gradient(135deg, #3a2a4a, #201520); }

/* Case Detail */
.case-detail-section { background: linear-gradient(135deg, #1a2a4a, #0d1520); position: relative; min-height: 60vh; display: flex; align-items: center; justify-content: center; }
.case-detail-section::after, .case-detail-body::after { display: none; }
.case-detail-content { position: relative; z-index: 2; max-width: 1100px; margin: 0 auto; padding: 8rem 4rem; text-align: center; color: #fff; }
.case-detail-body { background: #fff; position: relative; justify-content: center; min-height: auto; }
.case-detail-body::after { display: none; }
.case-detail-body-content { position: relative; z-index: 2; max-width: 1100px; margin: 0 auto; padding: 4rem; color: #000; }
.case-detail-content p, .case-detail-body-content p { font-size: 1rem; text-transform: uppercase; line-height: 1.8; margin-bottom: 2rem; color: #000; }
.case-detail-content h2, .case-detail-body-content h2 { font-family: var(--font-display); font-size: 1.5rem; font-weight: 700; text-transform: uppercase; letter-spacing: 0.96px; margin: 3rem 0 1.5rem; color: #000; }

/* Team */
.team-section { background: url('assets/Background.png') fixed center/cover; position: relative; }
.team-section::before { content: ''; position: absolute; inset: 0; background: rgba(255, 255, 255, 0.7); }
.team-content { position: relative; z-index: 2; max-width: 1100px; margin: 0 auto; padding: 8rem 4rem; }
.member-item { display: grid; grid-template-columns: 200px 1fr; gap: 3rem; margin-bottom: 4rem; padding-bottom: 4rem; border-bottom: 1px solid var(--glass-border); }
.member-item:last-child { border-bottom: none; }
.member-photo { width: 200px; height: 260px; border-radius: 4px; object-fit: cover; }
.member-info .name { font-family: var(--font-display); font-size: 1.5rem; font-weight: 700; letter-spacing: 0.96px; margin-bottom: 0.5rem; color: var(--white); }
.member-info .title { font-family: var(--font-body); font-size: 0.9rem; margin-bottom: 1.5rem; opacity: 0.7; color: var(--white); }
.member-info .bio { font-size: 0.95rem; line-height: 1.7; color: var(--white); }
.papers-section { padding: 4rem 0; border-top: 1px solid var(--glass-border); }
.paper-item { margin-bottom: 2rem; }
.paper-item .title { font-family: var(--font-display); font-size: 1rem; font-weight: 700; letter-spacing: 0.5px; margin-bottom: 0.5rem; color: var(--white); }
.paper-item .meta { font-size: 0.75rem; opacity: 0.6; margin-bottom: 1rem; color: var(--white); }

/* Download */
.download-section { min-height: 100vh; display: flex; align-items: center; justify-content: center; background: url('assets/Background.png') fixed center/cover; position: relative; }
.download-section::before { content: ''; position: absolute; inset: 0; background: rgba(255, 255, 255, 0.7); }
.download-content { position: relative; z-index: 2; text-align: center; padding: 4rem; }
.download-content .display-hero { margin-bottom: 1rem; color: var(--white); }
.download-content .body-text { margin-bottom: 3rem; color: var(--white); }
.download-btn { display: inline-block; padding: 18px 40px; font-family: var(--font-display); font-size: 0.81rem; font-weight: 700; text-transform: uppercase; letter-spacing: 1.17px; color: var(--black); background: var(--white); border-radius: 32px; transition: opacity 0.3s; border: 2px solid var(--white); }
.download-btn:hover { opacity: 0.8; }
.requirements { max-width: 700px; margin: 4rem auto 0; text-align: left; }
.requirements h3 { font-family: var(--font-display); font-size: 0.81rem; font-weight: 700; text-transform: uppercase; letter-spacing: 1.17px; margin-bottom: 2rem; color: var(--white); }
.req-item { margin-bottom: 1.5rem; }
.req-item h4 { font-family: var(--font-display); font-size: 0.75rem; font-weight: 700; text-transform: uppercase; letter-spacing: 1px; margin-bottom: 0.5rem; opacity: 0.7; color: var(--white); }
.req-item p { font-size: 0.9rem; text-transform: uppercase; color: var(--white); }

/* Tutorials */
.tutorials-section { min-height: 100vh; display: flex; align-items: center; justify-content: center; background: url('assets/Background.png') fixed center/cover; position: relative; }
.tutorials-section::before { content: ''; position: absolute; inset: 0; background: rgba(255, 255, 255, 0.7); }
.tutorials-content { position: relative; z-index: 2; text-align: center; padding: 4rem; }
.tutorials-content .display-hero { margin-bottom: 1rem; color: var(--white); }
.tutorials-content .body-text { margin-bottom: 3rem; color: var(--white); }

/* Publications */
.publications-page { padding: 8rem 4rem 4rem; }
.publications-page .display-hero { margin-bottom: 3rem; color: var(--white); }

/* Footer */
.footer { padding: 2rem 4rem; text-align: center; border-top: 1px solid var(--glass-border); background: var(--white); }
.footer p { font-size: 0.75rem; opacity: 0.5; color: var(--black); }
.footer img { height: 14px; vertical-align: middle; }

/* Mobile Menu */
.mobile-menu-toggle { display: none; flex-direction: column; justify-content: center; gap: 5px; cursor: pointer; padding: 10px; z-index: 1001; }
.mobile-menu-toggle span { width: 25px; height: 2px; background: var(--white); transition: all 0.3s; }
.mobile-menu-toggle.active span:nth-child(1) { transform: rotate(45deg) translate(5px, 5px); }
.mobile-menu-toggle.active span:nth-child(2) { opacity: 0; }
.mobile-menu-toggle.active span:nth-child(3) { transform: rotate(-45deg) translate(5px, -5px); }
.mobile-nav-overlay { display: none; position: fixed; inset: 0; background: rgba(255,255,255,0.95); z-index: 999; justify-content: center; align-items: center; }
.mobile-nav-overlay.active { display: flex; }
.mobile-nav-links { display: flex; flex-direction: column; gap: 2rem; text-align: center; }
.mobile-nav-links a { font-size: 1.2rem; font-weight: 600; letter-spacing: 2px; text-transform: uppercase; color: var(--white); }

/* Responsive */
@media (max-width: 1024px) {
    .navbar { padding: 1rem 2rem; }
    .nav-links { gap: 2rem; }
    .hero .display-hero { font-size: 3rem; }
    .display-hero { font-size: 2.5rem; }
    .cases-grid { padding: 6rem 2rem; }
    .card-content { padding: 3rem 2rem; }
    .card-content.right { margin-right: 2rem; }
}

@media (max-width: 768px) {
    .navbar { padding: 1rem 1.5rem; background: rgba(255,255,255,0.95); }
    .nav-links { display: none; }
    .mobile-menu-toggle { display: flex; }
    .mobile-menu-toggle span { background: var(--white); }
    .hero-content, .section-content { padding: 2rem; }
    .hero .display-hero { font-size: 2rem; }
    .display-hero { font-size: 1.8rem; }
    .hero .subtitle { font-size: 0.9rem; letter-spacing: 0; text-transform: none; }
    .body-text { text-transform: none; }
    .cases-grid { grid-template-columns: 1fr; padding: 4rem 1.5rem; }
    .case-card { min-height: 300px; }
    .case-card .card-title { font-size: 1.5rem; text-transform: none; }
    .case-card .card-desc { text-transform: none; font-size: 0.85rem; }
    .card-content, .card-content.right { padding: 2rem 1.5rem; margin-right: 1.5rem; }
    .member-item { grid-template-columns: 1fr; text-align: center; }
    .member-photo { margin: 0 auto 2rem; width: 150px; height: 200px; }
    .case-detail-section, .case-detail-body { justify-content: center; }
    .case-detail-content { padding: 6rem 1.5rem; }
    .case-detail-body-content { padding: 2rem 1.5rem; }
    .case-detail-content p, .case-detail-body-content p { text-transform: none; font-size: 0.9rem; }
    .download-content, .tutorials-content { padding: 2rem 1.5rem; }
    .hero-buttons { flex-direction: column; gap: 1rem; }
    .btn { width: 100%; text-align: center; }
    .download-btn { padding: 15px 30px; }
    .footer { padding: 2rem 1.5rem; }
    .footer p { font-size: 0.7rem; }
    .section { min-height: auto; padding: 6rem 0; }
    .requirements { padding: 0 1rem; }
    .req-item p { text-transform: none; }
    .publications-page { padding: 6rem 1.5rem 4rem; }
}