:root { --primary-blue: #2563eb; --accent-orange: #f97316; --font-sans: 'Inter', sans-serif; --border-radius: 8px; }
[data-theme="light"] { --bg-primary: #f8fafc; --bg-secondary: #ffffff; --surface: #f1f5f9; --text-primary: #0f172a; --text-secondary: #475569; --border: #e2e8f0; }
[data-theme="dark"] { --bg-primary: #0b1120; --bg-secondary: #1e293b; --surface: #334155; --text-primary: #f8fafc; --text-secondary: #94a3b8; --border: #475569; }

body { font-family: var(--font-sans); background-color: var(--bg-primary); color: var(--text-primary); margin: 0; line-height: 1.6; transition: background-color 0.3s, color 0.3s; }
h1, h2, h3, h4 { font-weight: 700; margin: 0; }
h1 { font-size: clamp(2rem, 5vw, 3rem); margin-bottom: 0.5rem; }
h2 { font-size: clamp(1.5rem, 4vw, 2rem); margin-bottom: 1rem; }
p { color: var(--text-secondary); margin: 0 0 1rem 0; }
a { color: var(--primary-blue); text-decoration: none; }
.container { max-width: 1200px; margin: 0 auto; padding: 0 20px; }
.section { padding: 40px 0; }
.section-header { text-align: center; margin-bottom: 40px; }

header { background-color: var(--bg-secondary); border-bottom: 1px solid var(--border); position: sticky; top: 0; z-index: 1000; transition: background-color 0.3s, border-color 0.3s; }
nav { display: flex; justify-content: space-between; align-items: center; height: 70px; max-width: 1200px; margin: 0 auto; padding: 0 20px; }
.logo { display: flex; align-items: center; font-weight: 600; font-size: 1.2rem; }
.logo i { margin-right: 10px; color: var(--primary-blue); }
.nav-links { display: flex; list-style: none; gap: 25px; margin: 0; padding: 0; align-items: center; }
.nav-link { font-weight: 500; color: var(--text-secondary); transition: color 0.2s; position: relative; padding: 5px 0; cursor: pointer; }
.nav-link::after { content: ''; position: absolute; bottom: 0; left: 0; width: 0; height: 2px; background: var(--primary-blue); transition: width 0.3s ease; }
.nav-link:hover::after, .nav-link.active::after { width: 100%; }
.nav-simulator-btn { background: var(--accent-orange); color: white !important; padding: 8px 12px; border-radius: var(--border-radius); transition: all 0.2s; }
.nav-simulator-btn:hover { transform: scale(1.05); }
.nav-simulator-btn::after { display: none; }
.nav-controls { display: flex; align-items: center; gap: 15px; }

.hero { display: flex; flex-wrap: wrap; justify-content: space-between; align-items: center; gap: 40px; padding: 40px 0; }
.hero-text { flex: 2; min-width: 300px; }
.hero-stats { display: grid; grid-template-columns: 1fr 1fr; gap: 20px; flex: 1; min-width: 280px; }
.stat { background-color: var(--bg-secondary); border: 1px solid var(--border); padding: 20px; border-radius: var(--border-radius); text-align: center; }
.stat-number { font-size: 2.5rem; font-weight: 700; color: var(--primary-blue); }
.stat-label { font-size: 0.9rem; color: var(--text-secondary); }

.search-container { position: relative; margin-top: 20px; }
.search-container i { position: absolute; left: 15px; top: 50%; transform: translateY(-50%); color: var(--text-secondary); }
#searchInput { width: 100%; padding: 12px 15px 12px 40px; border-radius: var(--border-radius); border: 1px solid var(--border); background-color: var(--bg-secondary); color: var(--text-primary); font-size: 1rem; box-sizing: border-box; }
.filter-buttons { display: flex; justify-content: center; gap: 10px; margin-bottom: 30px; flex-wrap: wrap; }
.filter-btn { padding: 10px 20px; border: 1px solid var(--border); background-color: var(--bg-secondary); color: var(--text-secondary); border-radius: 20px; cursor: pointer; transition: all 0.2s; }
.filter-btn:hover { background-color: var(--surface); color: var(--text-primary); }
.filter-btn.active { background-color: var(--primary-blue); color: white; border-color: var(--primary-blue); }

.grid-2, .grid-3 { display: grid; gap: 20px; }
.grid-2 { grid-template-columns: repeat(auto-fit, minmax(300px, 1fr)); }
.grid-3 { grid-template-columns: repeat(auto-fit, minmax(280px, 1fr)); }
.card { background-color: var(--bg-secondary); border: 1px solid var(--border); border-radius: var(--border-radius); padding: 20px; display: flex; flex-direction: column; cursor: pointer; transition: transform 0.3s, box-shadow 0.3s; }
.card:hover { transform: translateY(-5px) scale(1.02); box-shadow: 0 10px 20px rgba(0,0,0,0.08); }
.card-header { display: flex; justify-content: space-between; align-items: start; margin-bottom: 15px; }
.card-title { font-weight: 600; font-size: 1.1rem; color: var(--text-primary); }
.card-subtitle { font-size: 0.9rem; color: var(--text-secondary); }
.card-icon { font-size: 1.5rem; color: var(--primary-blue); }
.card-content { flex-grow: 1; }
.card-tags { display: flex; flex-wrap: wrap; gap: 8px; margin-top: 15px; }
.tag { background-color: var(--surface); color: var(--text-secondary); padding: 4px 10px; border-radius: 12px; font-size: 0.8rem; }
.composition-bar { display: flex; width: 100%; height: 20px; border-radius: 5px; overflow: hidden; margin: 10px 0; background-color: var(--surface); }
.composition-segment { height: 100%; }

.modal { display: none; position: fixed; z-index: 2000; left: 0; top: 0; width: 100%; height: 100%; overflow: auto; background-color: rgba(0,0,0,0.6); animation: fadeIn 0.3s ease; }
.modal-content { background-color: var(--bg-secondary); margin: 5% auto; padding: 30px; border-radius: var(--border-radius); max-width: 800px; position: relative; }
.modal-content.large { max-width: 900px; }
.modal-close-btn { color: var(--text-secondary); position: absolute; top: 15px; right: 20px; font-size: 28px; font-weight: bold; cursor: pointer; }

.credits { background-color: var(--bg-secondary); border-top: 1px solid var(--border); padding: 40px 0; text-align: center; }
.credits-info { display: flex; justify-content: center; margin-top: 20px; }
.main-credit { text-align: center; }
.credit-name { font-size: 1.2rem; font-weight: 600; color: var(--text-primary); }
.credit-title { font-size: 1rem; color: var(--text-secondary); margin-top: 4px; }
.contact-info { margin-top: 10px; }
.icon-link { color: var(--text-secondary); display: inline-flex; align-items: center; justify-content: center; gap: 8px; transition: color 0.2s; }
.icon-link:hover { color: var(--primary-blue); }
.credit-verified { margin-top: 15px; font-size: 0.9rem; color: var(--accent-orange); }

.progress-indicator { position: fixed; top: 0; left: 0; width: 100%; height: 4px; z-index: 2000; }
.progress-bar { width: 0; height: 100%; background-color: var(--primary-blue); }
.loading-screen { position: fixed; top: 0; left: 0; width: 100%; height: 100%; background: var(--bg-primary); display: flex; justify-content: center; align-items: center; flex-direction: column; z-index: 9999; transition: opacity 0.5s; }
.loading-screen.hidden { opacity: 0; pointer-events: none; }
.cement-mixer { width: 60px; height: 60px; border: 5px solid var(--primary-blue); border-top-color: transparent; border-radius: 50%; animation: spin 1s linear infinite; margin-bottom: 20px; }
@keyframes spin { to { transform: rotate(360deg); } }
@keyframes fadeIn { from { opacity: 0; } to { opacity: 1; } }
@keyframes fadeInUp { from { opacity: 0; transform: translateY(20px); } to { opacity: 1; transform: translateY(0); } }
.card, .section-header, .stat, .chart-container { opacity: 0; }
.card.animate-in, .section-header.animate-in, .stat.animate-in, .chart-container.animate-in { animation: fadeInUp 0.6s ease-out forwards; }
.hero-stats .stat:nth-child(1) { animation-delay: 0.1s; } .hero-stats .stat:nth-child(2) { animation-delay: 0.2s; } .hero-stats .stat:nth-child(3) { animation-delay: 0.3s; }

.chart-grid { margin-top: 40px; }
.chart-container { background: var(--bg-secondary); padding: 20px; border-radius: var(--border-radius); border: 1px solid var(--border); position: relative; height: 450px; width: 100%; }
.calculator-grid, .engine-grid { display: grid; grid-template-columns: 1fr 1fr; gap: 30px; margin-top: 20px; }
.input-group { margin-bottom: 15px; }
.input-group label { display: block; font-weight: 500; color: var(--text-secondary); margin-bottom: 5px; }
.input-group input, .input-group select { width: 100%; padding: 10px; border-radius: 5px; border: 1px solid var(--border); background-color: var(--surface); color: var(--text-primary); box-sizing: border-box; }
.calculate-btn { width: 100%; padding: 12px; background-color: var(--primary-blue); color: white; border: none; border-radius: 5px; font-size: 1rem; cursor: pointer; margin-top: 20px; }
#calculatorResults, #engineResults { background-color: var(--surface); padding: 20px; border-radius: 10px; }
#calculatorContent h3, #engineContent h3, .engine-title { color: var(--primary-blue); margin-bottom: 20px; border-bottom: 2px solid var(--primary-blue); padding-bottom: 10px; }
#calculatorResults h4, #engineResults h4 { color: var(--accent-orange); margin-bottom: 15px; }
.launch-calculator-btn { display: inline-block; margin-top: 20px; padding: 10px 15px; background-color: var(--accent-orange); color: white; border-radius: 5px; cursor: pointer; text-align: center; }
.info-box { background: var(--surface); margin: 15px 0; padding: 20px; border-radius: 10px; border: 1px solid var(--border); }
.info-box h5 { color: var(--primary-blue); margin-bottom: 15px; }
.strength-variant-grid { display: grid; grid-template-columns: repeat(auto-fit, minmax(200px, 1fr)); gap: 15px; }
.strength-variant-card { padding: 15px; border-radius: 8px; border: 2px solid var(--border); }
.strength-variant-card.disabled { opacity: 0.5; }
.strength-variant-card:not(.disabled) { border-color: var(--primary-blue); }
.strength-variant-card h6 { color: var(--text-secondary); margin-bottom: 10px; }
.strength-variant-card:not(.disabled) h6 { color: var(--primary-blue); }
.strength-variant-card ul { font-size: 0.85rem; padding-left: 20px; margin: 0; }

.mobile-menu { display: none; }
@media (max-width: 820px) {
    .nav-links { display: none; position: absolute; top: 70px; left: 0; width: 100%; background: var(--bg-secondary); flex-direction: column; text-align: center; padding: 10px 0; box-shadow: 0 4px 6px rgba(0,0,0,0.1); }
    .nav-links.active { display: flex; }
    .mobile-menu { display: flex; flex-direction: column; cursor: pointer; gap: 5px; padding: 8px; }
    .mobile-menu span { height: 2px; width: 25px; background: var(--text-primary); transition: all 0.3s; }
    .mobile-menu.active span:nth-child(1) { transform: rotate(45deg) translate(5px, 5px); }
    .mobile-menu.active span:nth-child(2) { opacity: 0; }
    .mobile-menu.active span:nth-child(3) { transform: rotate(-45deg) translate(5px, -5px); }
    .hero { flex-direction: column; text-align: center;}
    .hero-text { order: 2; } .hero-stats { order: 1; }
    .calculator-grid, .engine-grid { grid-template-columns: 1fr; }
}