/* EnergyFusion - Renewable Energy Engineering Platform */
:root {
  --primary: #0d47a1;
  --primary-dark: #002171;
  --primary-light: #5472d3;
  --accent: #00c853;
  --bg: #f5f7fa;
  --card: #ffffff;
  --text: #1a1a2e;
  --text-light: #546e7a;
  --border: #e0e6ed;
  --hero-from: #0d1b3e;
  --hero-to: #1a3a6b;
  --cta-bg: #e8f0fe;
  --cta-border: #1a73e8;
  --radius: 8px;
}

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

body { font-family: 'Segoe UI', system-ui, -apple-system, sans-serif; background: var(--bg); color: var(--text); line-height: 1.6; }

/* Navbar */
.navbar { background: var(--primary-dark); color: #fff; padding: 0 24px; position: sticky; top: 0; z-index: 1000; display: flex; align-items: center; justify-content: space-between; height: 60px; box-shadow: 0 2px 8px rgba(0,0,0,0.15); }
.navbar .logo { font-size: 1.4rem; font-weight: 700; letter-spacing: 0.5px; }
.navbar .logo span { color: var(--accent); }
.navbar nav { display: flex; gap: 20px; }
.navbar nav a { color: #cfd8e6; text-decoration: none; font-size: 0.9rem; padding: 8px 12px; border-radius: 4px; transition: all 0.2s; }
.navbar nav a:hover { color: #fff; background: rgba(255,255,255,0.1); }
.navbar .hamburger { display: none; flex-direction: column; gap: 5px; cursor: pointer; background: none; border: none; padding: 8px; }
.navbar .hamburger span { display: block; width: 24px; height: 3px; background: #fff; border-radius: 2px; }

/* Hero */
.hero { background: linear-gradient(135deg, var(--hero-from) 0%, var(--hero-to) 50%, #1e5799 100%); color: #fff; padding: 80px 24px 60px; text-align: center; }
.hero h1 { font-size: 2.8rem; font-weight: 800; margin-bottom: 12px; letter-spacing: -0.5px; }
.hero h1 span { color: var(--accent); }
.hero .subtitle { font-size: 1.15rem; color: #b0c4de; max-width: 700px; margin: 0 auto 32px; }
.hero .search-box { max-width: 560px; margin: 0 auto; position: relative; }
.hero .search-box input { width: 100%; padding: 16px 20px; font-size: 1rem; border: 2px solid transparent; border-radius: 50px; outline: none; box-shadow: 0 4px 20px rgba(0,0,0,0.3); transition: border 0.2s; }
.hero .search-box input:focus { border-color: var(--accent); }

/* Container */
.container { max-width: 1200px; margin: 0 auto; padding: 0 24px; }

/* Section */
.section { padding: 48px 0; }
.section-title { font-size: 1.6rem; font-weight: 700; margin-bottom: 24px; color: var(--primary-dark); border-left: 4px solid var(--primary); padding-left: 16px; }

/* Card Grid */
.card-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(260px, 1fr)); gap: 20px; }
.card-grid.col2 { grid-template-columns: repeat(2, 1fr); }
.card-grid.col3 { grid-template-columns: repeat(3, 1fr); }
.card-grid.col4 { grid-template-columns: repeat(4, 1fr); }

/* Card */
.card { background: var(--card); border-radius: var(--radius); padding: 24px; box-shadow: 0 2px 12px rgba(0,0,0,0.06); border: 1px solid var(--border); transition: transform 0.2s, box-shadow 0.2s; text-decoration: none; color: var(--text); display: block; }
.card:hover { transform: translateY(-3px); box-shadow: 0 6px 24px rgba(0,0,0,0.1); }
.card .card-icon { font-size: 2rem; margin-bottom: 12px; }
.card .card-title { font-weight: 700; font-size: 1.05rem; margin-bottom: 6px; }
.card .card-desc { font-size: 0.85rem; color: var(--text-light); }
.card.star { border-left: 4px solid #ffa000; }
.card.accent { border-left: 4px solid var(--accent); }

/* CTA Card */
.cta-card { background: var(--cta-bg); border: 2px solid var(--cta-border); border-radius: var(--radius); padding: 24px; text-align: center; margin: 24px 0; }
.cta-card p { font-size: 1.1rem; margin-bottom: 12px; color: var(--primary-dark); }
.cta-card .btn { display: inline-block; }

/* Button */
.btn { background: var(--primary); color: #fff; padding: 12px 28px; border-radius: 50px; text-decoration: none; font-weight: 600; font-size: 0.95rem; display: inline-block; transition: background 0.2s; border: none; cursor: pointer; }
.btn:hover { background: var(--primary-dark); }
.btn-outline { background: transparent; border: 2px solid var(--primary); color: var(--primary); }
.btn-outline:hover { background: var(--primary); color: #fff; }
.btn-accent { background: var(--accent); }
.btn-accent:hover { background: #00a844; }

/* Calculator Area */
.calc-container { background: var(--card); border-radius: var(--radius); padding: 32px; box-shadow: 0 2px 16px rgba(0,0,0,0.08); margin-bottom: 32px; }
.calc-container h3 { margin-bottom: 20px; color: var(--primary-dark); }
.calc-row { display: flex; gap: 16px; align-items: flex-end; flex-wrap: wrap; margin-bottom: 16px; }
.calc-row label { display: block; font-size: 0.85rem; font-weight: 600; margin-bottom: 4px; color: var(--text-light); }
.calc-row input, .calc-row select { padding: 10px 14px; border: 1px solid var(--border); border-radius: 6px; font-size: 1rem; width: 160px; }
.calc-row input:focus, .calc-row select:focus { border-color: var(--primary); outline: none; box-shadow: 0 0 0 3px rgba(13,71,161,0.1); }
.calc-result { background: #e8f5e9; border-radius: var(--radius); padding: 20px; margin-top: 20px; }
.calc-result .result-value { font-size: 2rem; font-weight: 700; color: #2e7d32; }
.calc-result .result-label { font-size: 0.85rem; color: var(--text-light); }

/* Content Area */
.content { max-width: 800px; margin: 0 auto; }
.content h2 { font-size: 1.5rem; margin: 32px 0 16px; color: var(--primary-dark); border-bottom: 2px solid var(--border); padding-bottom: 8px; }
.content h3 { font-size: 1.2rem; margin: 24px 0 12px; color: var(--primary-light); }
.content p { margin-bottom: 16px; }
.content ul, .content ol { margin: 0 0 16px 24px; }
.content li { margin-bottom: 6px; }

/* Formula Block */
.formula-block { background: #1a1a2e; color: #a8d8ea; padding: 16px 24px; border-radius: var(--radius); font-family: 'Courier New', monospace; font-size: 1.1rem; margin: 16px 0; overflow-x: auto; }

/* Table */
.table-wrap { overflow-x: auto; margin: 16px 0; }
table { width: 100%; border-collapse: collapse; font-size: 0.9rem; }
table th { background: var(--primary-dark); color: #fff; padding: 12px 16px; text-align: left; font-weight: 600; }
table td { padding: 10px 16px; border-bottom: 1px solid var(--border); }
table tr:nth-child(even) { background: #f8f9fb; }
table tr:hover { background: #e8f0fe; }

/* FAQ */
.faq-list { margin: 24px 0; }
.faq-item { border: 1px solid var(--border); border-radius: var(--radius); margin-bottom: 8px; overflow: hidden; }
.faq-question { width: 100%; text-align: left; padding: 16px 20px; background: var(--card); border: none; font-size: 1rem; font-weight: 600; cursor: pointer; display: flex; justify-content: space-between; align-items: center; color: var(--text); }
.faq-question:hover { background: #f0f4f8; }
.faq-question .arrow { transition: transform 0.3s; font-size: 0.8rem; }
.faq-question.open .arrow { transform: rotate(180deg); }
.faq-answer { padding: 0 20px; max-height: 0; overflow: hidden; transition: max-height 0.3s ease, padding 0.3s ease; background: #fafbfc; }
.faq-answer.open { max-height: 300px; padding: 16px 20px; }

/* Mistakes */
.mistake-list { margin: 16px 0; }
.mistake-item { display: flex; gap: 12px; padding: 12px 16px; margin-bottom: 8px; border-radius: var(--radius); align-items: flex-start; }
.mistake-item.bad { background: #ffebee; border-left: 4px solid #d32f2f; }
.mistake-item.good { background: #e8f5e9; border-left: 4px solid #2e7d32; }
.mistake-item .tag { font-weight: 700; min-width: 24px; }

/* Footer */
.footer { background: var(--primary-dark); color: #90a4ae; padding: 40px 24px 24px; margin-top: 60px; }
.footer-grid { max-width: 1200px; margin: 0 auto; display: grid; grid-template-columns: repeat(auto-fit, minmax(200px, 1fr)); gap: 32px; }
.footer h4 { color: #fff; margin-bottom: 12px; font-size: 0.95rem; }
.footer a { color: #90a4ae; text-decoration: none; font-size: 0.85rem; display: block; margin-bottom: 6px; }
.footer a:hover { color: #fff; }
.footer-bottom { max-width: 1200px; margin: 32px auto 0; padding-top: 16px; border-top: 1px solid rgba(255,255,255,0.1); text-align: center; font-size: 0.8rem; }

/* Breadcrumb */
.breadcrumb { padding: 12px 0; font-size: 0.85rem; color: var(--text-light); }
.breadcrumb a { color: var(--primary); text-decoration: none; }
.breadcrumb a:hover { text-decoration: underline; }

/* Responsive */
@media (max-width: 768px) {
  .navbar nav { display: none; position: absolute; top: 60px; left: 0; right: 0; background: var(--primary-dark); flex-direction: column; padding: 12px; }
  .navbar nav.open { display: flex; }
  .navbar .hamburger { display: flex; }
  .hero h1 { font-size: 1.8rem; }
  .hero { padding: 48px 16px 36px; }
  .card-grid { grid-template-columns: 1fr; }
  .card-grid.col2, .card-grid.col3, .card-grid.col4 { grid-template-columns: 1fr; }
  .calc-row { flex-direction: column; }
  .calc-row input, .calc-row select { width: 100%; }
  .content { padding: 0 16px; }
}

@media print {
  .navbar, .footer, .hero, .cta-card { display: none; }
  body { background: #fff; }
  .card { box-shadow: none; border: 1px solid #ddd; }
}