* { margin: 0; padding: 0; box-sizing: border-box; }
body { font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', system-ui, sans-serif; line-height: 1.6; color: #333; }
.container { max-width: 1200px; margin: 0 auto; padding: 0 20px; }

header { background: linear-gradient(135deg, #ffffff 0%, #f8fafc 100%); box-shadow: 0 4px 20px rgba(0,0,0,0.08); position: sticky; top: 0; z-index: 100; border-bottom: 1px solid #e2e8f0; }
nav { display: flex; justify-content: space-between; align-items: center; padding: 1.5rem 0; }
.logo { display: flex; align-items: center; gap: 0.75rem; font-size: 1.75rem; font-weight: 800; color: #1e40af; text-decoration: none; transition: transform 0.2s; }
.logo:hover { transform: scale(1.02); }
.nav-links { display: flex; list-style: none; }
.nav-links a { text-decoration: none; color: #4b5563; font-weight: 600; font-size: 1rem; transition: all 0.3s; padding: 0.5rem 1rem; border-radius: 8px; }
.nav-links a:hover { color: #1e40af; background: #dbeafe; }

.mobile-menu-btn { display: none; background: none; border: none; cursor: pointer; padding: 0.5rem; }
.mobile-menu-btn span { display: block; width: 25px; height: 3px; background: #4b5563; margin: 5px 0; transition: 0.3s; }
.mobile-menu-btn.active span:nth-child(1) { transform: rotate(-45deg) translate(-5px, 6px); }
.mobile-menu-btn.active span:nth-child(2) { opacity: 0; }
.mobile-menu-btn.active span:nth-child(3) { transform: rotate(45deg) translate(-5px, -6px); }

.mobile-menu { display: none; position: absolute; top: 100%; left: 0; right: 0; background: white; box-shadow: 0 4px 20px rgba(0,0,0,0.1); border-top: 1px solid #e2e8f0; }
.mobile-menu.active { display: block; }
.mobile-menu ul { list-style: none; padding: 1rem 0; }
.mobile-menu li { border-bottom: 1px solid #f1f5f9; }
.mobile-menu a { display: block; padding: 1rem 1.5rem; color: #4b5563; text-decoration: none; font-weight: 600; transition: background 0.3s; }
.mobile-menu a:hover { background: #f8fafc; color: #1e40af; }

.hero { background: linear-gradient(135deg, #667eea 0%, #764ba2 100%); color: white; padding: 4rem 0; text-align: center; }
.hero h1 { font-size: 3rem; margin-bottom: 1rem; font-weight: 700; }
.hero .subtitle { font-size: 1.25rem; margin-bottom: 2rem; opacity: 0.9; max-width: 600px; margin-left: auto; margin-right: auto; }
.cta-button { display: inline-block; background: #f59e0b; color: white; padding: 1rem 2rem; border-radius: 8px; font-size: 1.1rem; font-weight: 600; text-decoration: none; transition: transform 0.2s, box-shadow 0.2s; }
.cta-button:hover { transform: translateY(-2px); box-shadow: 0 10px 25px rgba(0,0,0,0.2); }

.today-preview { background: #f8fafc; padding: 2rem 0; }
.preview-card { background: white; border-radius: 12px; padding: 2rem; box-shadow: 0 4px 20px rgba(0,0,0,0.1); max-width: 1000px; margin: 0 auto; }
.preview-header { display: flex; justify-content: space-between; align-items: center; margin-bottom: 1.5rem; }
.difficulty { background: #10b981; color: white; padding: 0.25rem 0.75rem; border-radius: 20px; font-size: 0.875rem; }
.difficulty.medium { background: #f59e0b; }
.difficulty.hard { background: #ef4444; }
.spoiler-warning { background: #fef3c7; border: 2px solid #f59e0b; border-radius: 8px; padding: 1rem; margin-bottom: 1.5rem; text-align: center; }
.hints-preview { margin-bottom: 2rem; }
.hint { background: #f1f5f9; padding: 1rem; margin-bottom: 0.5rem; border-radius: 6px; border-left: 4px solid #2563eb; }

.difficulty-tabs { display: flex; gap: 0.5rem; border: 1px solid #e2e8f0; border-radius: 25px; padding: 0.25rem; background-color: #f1f5f9; }
.tab-link { flex: 1;padding: 0.5rem 1rem; border: none; background: transparent; border-radius: 20px; font-weight: 600; cursor: pointer; transition: all 0.3s; color: #4b5563; }
.tab-link:hover { background-color: #e2e8f0; }
.tab-link.active { background-color: #ef4444; color: white; box-shadow: 0 2px 10px rgba(0,0,0,0.1); }
#easy .tab-link.active { background-color: #10b981; }
#medium .tab-link.active { background-color: #f59e0b; }
#hard .tab-link.active { background-color: #ef4444; }
.difficulty-content { display: none; margin-top: 1.5rem; }
.preview-subheader { margin-bottom: 1.5rem; }
.difficulty.easy { background: #10b981; }

.features { padding: 2rem 0; }
.features h2 { text-align: center; margin-bottom: 1rem; font-size: 2rem; }
.features-intro { text-align: center; margin-bottom: 3rem; max-width: 600px; margin-left: auto; margin-right: auto; color: #6b7280; }
.features-grid { display: grid; grid-template-columns: repeat(auto-fit, minmax(300px, 1fr)); gap: 2rem; }
.feature-card { text-align: center; padding: 2rem; border-radius: 12px; transition: transform 0.3s; }
.feature-card:hover { transform: translateY(-5px); }
.feature-icon { width: 64px; height: 64px; background: #2563eb; border-radius: 50%; margin: 0 auto 1.5rem; display: flex; align-items: center; justify-content: center; font-size: 1.5rem; color: white; }
.feature-card h3 { margin-bottom: 1rem; font-size: 1.25rem; }

.recent-solutions { background: #f8fafc; padding: 3rem 0; }
.solutions-grid { display: grid; grid-template-columns: repeat(auto-fit, minmax(250px, 1fr)); gap: 1.5rem; margin-top: 2rem; }
.solution-card { background: white; border-radius: 8px; padding: 1.5rem; box-shadow: 0 2px 10px rgba(0,0,0,0.1); transition: transform 0.2s; }
.solution-card:hover { transform: translateY(-2px); }
.solution-date { font-weight: 600; color: #2563eb; margin-bottom: 0.5rem; }
.solution-link { color: #2563eb; text-decoration: none; font-weight: 500; }
.solution-link::after {content: 'View Answer →';}

.stats { padding: 3rem 0; text-align: center; }
.stats-grid { display: grid; grid-template-columns: repeat(auto-fit, minmax(200px, 1fr)); gap: 2rem; margin-top: 2rem; }
.stat { padding: 2rem; }
.stat-number { font-size: 2.5rem; font-weight: 700; color: #2563eb; }
.stat-label { font-size: 1rem; color: #666; margin-top: 0.5rem; }

footer { background: linear-gradient(135deg, #1f2937 0%, #111827 100%); color: white; padding: 3rem 0 2rem; }
.footer-content { display: grid; grid-template-columns: repeat(6, 1fr); gap: 3rem; margin-bottom: 2rem; }
.footer-section h3 { margin-bottom: 1.5rem; font-size: 1.25rem; color: #f3f4f6; }
.footer-section h4 { margin-bottom: 0.25rem; font-size: 1rem; color: #f3f4f6; }
.footer-section.brand { display: flex; flex-direction: column; gap: 1rem; }
.footer-section:first-child { grid-column: span 2; }
.footer-section:last-child { grid-column: span 2; }
.footer-logo { display: flex; align-items: center; gap: 0.75rem; margin-bottom: 1rem; }
.footer-logo-text { font-size: 1.5rem; font-weight: 700; color: #f3f4f6; }
.footer-links { list-style: none; }
.footer-links li { margin-bottom: 0.75rem; }
.footer-links a { color: #9ca3af; text-decoration: none; transition: color 0.3s; }
.footer-links a:hover { color: #f3f4f6; }
.footer-bottom { border-top: 1px solid #374151; padding-top: 2rem; text-align: center; color: #9ca3af; }

.newsletter-form { display: flex; border-radius: 8px; overflow: hidden; max-width: 320px; border: 1px solid #4b5563; }
.newsletter-form input[type="email"] {flex-grow: 1; padding: 0.75rem; border: none; background-color: #374151; color: white; font-size: 1rem; min-width: 0; }
.newsletter-form input[type="email"]::placeholder { color: #9ca3af; }
.newsletter-form input[type="email"]:focus { outline: none; box-shadow: 0 0 0 2px #2563eb; z-index: 1; }
.newsletter-form button[type="submit"] { padding: 0.75rem 1.25rem; border: none; background-color: #2563eb; color: white; font-weight: 600; font-size: 1rem; cursor: pointer; transition: background-color 0.3s; }
.newsletter-form button[type="submit"]:hover { background-color: #1d4ed8; }

.social-links { display: column; gap: 1.5rem; }
.sr-only { position: absolute; width: 1px; height: 1px; padding: 0; margin: -1px; overflow: hidden; clip: rect(0, 0, 0, 0); white-space: nowrap; border-width: 0; }

.breadcrumb { display: block; background: white; border-bottom: 1px solid #e5e7eb; padding: 0.75rem 0; position: sticky; top: 0; z-index: 40; }
.breadcrumb-nav { display: flex; align-items: center; gap: 0.5rem; font-size: 0.875rem; }
.breadcrumb-link { color: #6b7280; text-decoration: none; padding: 0.25rem 0.5rem; border-radius: 4px; transition: all 0.2s; }
.breadcrumb-link:hover { color: #2563eb; background: #f3f4f6; }
.breadcrumb-separator { color: #d1d5db; }
.breadcrumb-current { color: #1f2937; font-weight: 500; }

.calendar-btn{background:#2563eb;color:white;border:none;padding:.6rem 1.25rem;border-radius:8px;font-weight:500;cursor:pointer;transition:background-color .3s;display:flex;align-items:center;gap:.5rem}
.calendar-btn:hover{background:#1d4ed8}
.calendar-wrapper { position:relative;display:flex;margin-bottom:15px;margin-top:10px;}
#date-picker.visually-hidden { position: absolute; top: 0; left: 0; opacity: 0; cursor: pointer; border: none; margin: 0; padding: 0; }
.solver-section { padding: 2rem 0; border-radius: 5px; background: linear-gradient(135deg, #3b82f6 0%, #2563eb 100%); }
.editor-section { text-align: center; background: linear-gradient(135deg, #10b981 0%, #059669 100%); color: white; padding: 2rem 0; max-width: 1200px; margin: auto; border-radius: 5px; }
.editor-section .section-title { color: white; font-size: 2rem; }
.editor-section .section-subtitle { color: rgba(255,255,255,0.95); }
.editor-steps { display: grid; grid-template-columns: repeat(auto-fit, minmax(250px, 1fr)); gap: 2rem; margin: 1rem 0; }
.step-card { background: rgba(255,255,255,0.15); border: 2px solid rgba(255,255,255,0.3); border-radius: 12px; padding: 1rem; text-align: center; backdrop-filter: blur(10px); }
.step-icon { font-size: 2rem; margin-bottom: 1rem; }
.step-card h3 { font-size: 1.5rem; margin-bottom: 0.5rem; }
.feature-card { background: white; border-radius: 12px; padding: 2rem; box-shadow: 0 4px 12px rgba(0,0,0,0.08); transition: transform 0.3s, box-shadow 0.3s;}

@media (max-width: 768px) {
    .hero {padding: 2rem 0;}
    .hero h1 { font-size: 2rem; }
    .nav-links { display: none; }
    .mobile-menu-btn { display: block; }
    .logo { font-size: 1.5rem; }
    .h5-hidden { display: none; }
    nav { padding: 1.25rem 0; position: relative; }
    .preview-header { flex-direction: column; gap: 1rem; }
    .footer-content { grid-template-columns: 1fr; gap: 2rem; }
    .footer-logo { justify-content: left; }
    .footer-bottom { text-align: center; }
    .container {padding-left: 5px;padding-right: 5px;}
    .preview-card { padding-left: 10px; padding-right: 10px; }
    .today-preview { padding-left:0; padding-right:0; padding-top: 1.5rem;}
}

.hero-nav { position: fixed; right: 0; top: 50%; transform: translateY(-50%) translateX(calc(100% - 16px)); z-index: 1000; transition: transform 0.4s cubic-bezier(0.4, 0, 0.2, 1); }
.hero-nav:hover { transform: translateY(-50%) translateX(0); }
.nav-items { display: flex; flex-direction: column; gap: 0.5rem; background: linear-gradient(135deg, rgba(102, 126, 234, 0.95) 0%, rgba(118, 75, 162, 0.95) 100%); backdrop-filter: blur(10px); padding: 1.5rem; border-radius: 20px 0 0 20px; box-shadow: -8px 8px 32px rgba(102, 126, 234, 0.3); }
.nav-items a { display: flex; align-items: center; gap: 1rem; padding: 1rem 1.25rem; background: rgba(255, 255, 255, 0.15); backdrop-filter: blur(5px); color: white; text-decoration: none; font-weight: 500; font-size: 0.9rem; border-radius: 12px; transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1); white-space: nowrap; border: 1px solid rgba(255, 255, 255, 0.2); position: relative; overflow: hidden; }
.nav-items a::before { content: ''; position: absolute; top: 0; left: -100%; width: 100%; height: 100%; background: linear-gradient(90deg, transparent, rgba(255, 255, 255, 0.3), transparent); transition: left 0.5s ease; }
.nav-items a:hover::before { left: 100%; }
.nav-items a:hover { background: rgba(255, 255, 255, 0.25); transform: translateX(-8px); border-color: rgba(255, 255, 255, 0.4); box-shadow: 0 4px 16px rgba(0, 0, 0, 0.2); }
.nav-items a span { font-weight: 600; letter-spacing: 0.3px; text-shadow: 0 2px 4px rgba(0, 0, 0, 0.2); }
.nav-items a:nth-child(1):hover { background: rgba(102, 126, 234, 0.4); }
.nav-items a:nth-child(2):hover { background: rgba(240, 147, 251, 0.4); }
.nav-items a:nth-child(3):hover { background: rgba(79, 172, 254, 0.4); }
.nav-items a:nth-child(4):hover { background: rgba(67, 233, 123, 0.4); }
.nav-items a:nth-child(5):hover { background: rgba(250, 112, 154, 0.4); }
.nav-items::before { content: ''; position: absolute; left: 0; top: 50%; transform: translateY(-50%); width: 4px; height: 60%; background: linear-gradient(180deg, transparent, rgba(255, 255, 255, 0.8), transparent); border-radius: 2px; animation: pulse 2s ease-in-out infinite; }
@keyframes pulse {
    0%, 100% { opacity: 0.5; }
    50% { opacity: 1; }
}
@media (max-width: 768px) {
    .hero-nav {transform: translateY(-50%) translateX(calc(100% - 12px)); }
    .nav-items { padding: 1rem; }
    .nav-items a { padding: 0.875rem 1rem; font-size: 0.85rem; }
}