/* Reset and Base Styles */
* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

body {
    font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
    line-height: 1.6;
    color: #1a202c;
    background: linear-gradient(135deg, #f7fafc 0%, #edf2f7 100%);
    overflow-x: hidden;
}

.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 20px;
}

/* Header */
.header {
    background: rgba(255, 255, 255, 0.95);
    backdrop-filter: blur(20px);
    box-shadow: 0 8px 32px rgba(0, 0, 0, 0.1);
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    z-index: 1000;
    transition: all 0.4s cubic-bezier(0.4, 0, 0.2, 1);
    border-bottom: 1px solid rgba(255, 255, 255, 0.2);
}

.header-content {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 1.2rem 0;
}

.logo {
    display: flex;
    align-items: center;
    font-size: 1.6rem;
    font-weight: 800;
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
    transition: all 0.3s ease;
}

.logo:hover {
    transform: scale(1.05);
}

.logo i {
    margin-right: 0.6rem;
    font-size: 2rem;
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.nav {
    display: flex;
    gap: 2.5rem;
}

.nav-link {
    text-decoration: none;
    color: #4a5568;
    font-weight: 600;
    font-size: 1rem;
    transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
    position: relative;
    padding: 0.5rem 0;
}

.nav-link::before {
    content: '';
    position: absolute;
    bottom: 0;
    left: 50%;
    width: 0;
    height: 3px;
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    border-radius: 2px;
    transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
    transform: translateX(-50%);
}

.nav-link:hover,
.nav-link.active {
    color: #667eea;
    transform: translateY(-2px);
}

.nav-link:hover::before,
.nav-link.active::before {
    width: 100%;
}

/* Hero Section */
.hero {
    background: linear-gradient(135deg, #667eea 0%, #764ba2 50%, #f093fb 100%);
    color: white;
    padding: 140px 0 100px;
    text-align: center;
    position: relative;
    overflow: hidden;
}

.hero::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background: url('data:image/svg+xml,<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 100 100"><defs><pattern id="grain" width="100" height="100" patternUnits="userSpaceOnUse"><circle cx="25" cy="25" r="1" fill="rgba(255,255,255,0.1)"/><circle cx="75" cy="75" r="1" fill="rgba(255,255,255,0.1)"/><circle cx="50" cy="10" r="0.5" fill="rgba(255,255,255,0.05)"/><circle cx="20" cy="80" r="0.5" fill="rgba(255,255,255,0.05)"/></pattern></defs><rect width="100" height="100" fill="url(%23grain)"/></svg>');
    opacity: 0.3;
}

.hero-content {
    max-width: 900px;
    margin: 0 auto;
    position: relative;
    z-index: 1;
}

.hero-title {
    font-size: 4rem;
    font-weight: 900;
    margin-bottom: 2rem;
    line-height: 1.1;
    text-shadow: 0 4px 20px rgba(0, 0, 0, 0.3);
    animation: fadeInUp 1s ease-out;
}

.hero-subtitle {
    font-size: 1.4rem;
    margin-bottom: 3.5rem;
    opacity: 0.95;
    line-height: 1.7;
    font-weight: 400;
    text-shadow: 0 2px 10px rgba(0, 0, 0, 0.2);
    animation: fadeInUp 1s ease-out 0.2s both;
}

.hero-stats {
    display: flex;
    justify-content: center;
    gap: 5rem;
    margin-bottom: 4rem;
    animation: fadeInUp 1s ease-out 0.4s both;
}

.stat {
    text-align: center;
    position: relative;
}

.stat::before {
    content: '';
    position: absolute;
    top: -10px;
    left: 50%;
    width: 60px;
    height: 60px;
    background: rgba(255, 255, 255, 0.1);
    border-radius: 50%;
    transform: translateX(-50%);
    z-index: -1;
}

.stat-number {
    display: block;
    font-size: 3rem;
    font-weight: 900;
    margin-bottom: 0.5rem;
    text-shadow: 0 2px 10px rgba(0, 0, 0, 0.3);
}

.stat-label {
    font-size: 1.1rem;
    opacity: 0.9;
    font-weight: 500;
}

.cta-button {
    display: inline-flex;
    align-items: center;
    gap: 0.8rem;
    background: rgba(255, 255, 255, 0.95);
    color: #667eea;
    padding: 1.2rem 2.5rem;
    border-radius: 60px;
    text-decoration: none;
    font-weight: 700;
    font-size: 1.2rem;
    transition: all 0.4s cubic-bezier(0.4, 0, 0.2, 1);
    box-shadow: 0 10px 40px rgba(0, 0, 0, 0.2);
    backdrop-filter: blur(10px);
    border: 1px solid rgba(255, 255, 255, 0.3);
    animation: fadeInUp 1s ease-out 0.6s both;
}

.cta-button:hover {
    transform: translateY(-5px) scale(1.05);
    box-shadow: 0 20px 60px rgba(0, 0, 0, 0.3);
    background: rgba(255, 255, 255, 1);
}

.cta-button i {
    transition: transform 0.3s ease;
}

.cta-button:hover i {
    transform: translateX(3px);
}

/* Papers Section */
.papers-section {
    padding: 100px 0;
    background: linear-gradient(135deg, #f7fafc 0%, #edf2f7 100%);
    position: relative;
}

.section-header {
    text-align: center;
    margin-bottom: 5rem;
}

.section-title {
    font-size: 3rem;
    font-weight: 800;
    background: linear-gradient(135deg, #2d3748 0%, #4a5568 100%);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
    margin-bottom: 1.5rem;
    position: relative;
}

.section-title::after {
    content: '';
    position: absolute;
    bottom: -10px;
    left: 50%;
    width: 80px;
    height: 4px;
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    border-radius: 2px;
    transform: translateX(-50%);
}

.section-subtitle {
    font-size: 1.3rem;
    color: #718096;
    max-width: 700px;
    margin: 0 auto;
    font-weight: 400;
}

/* Filter Tabs */
.filter-tabs {
    display: flex;
    justify-content: center;
    gap: 1.5rem;
    margin-bottom: 4rem;
    flex-wrap: wrap;
}

.filter-tab {
    background: rgba(255, 255, 255, 0.8);
    backdrop-filter: blur(10px);
    border: 2px solid rgba(102, 126, 234, 0.2);
    color: #4a5568;
    padding: 1rem 2rem;
    border-radius: 50px;
    font-weight: 600;
    font-size: 1rem;
    cursor: pointer;
    transition: all 0.4s cubic-bezier(0.4, 0, 0.2, 1);
    position: relative;
    overflow: hidden;
}

.filter-tab::before {
    content: '';
    position: absolute;
    top: 0;
    left: -100%;
    width: 100%;
    height: 100%;
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    transition: left 0.4s cubic-bezier(0.4, 0, 0.2, 1);
    z-index: -1;
}

.filter-tab:hover,
.filter-tab.active {
    color: white;
    border-color: transparent;
    transform: translateY(-3px);
    box-shadow: 0 10px 30px rgba(102, 126, 234, 0.4);
}

.filter-tab:hover::before,
.filter-tab.active::before {
    left: 0;
}

/* Subject Categories */
.subject-category {
    margin-bottom: 5rem;
    animation: fadeInUp 0.8s ease-out;
}

.category-title {
    display: flex;
    align-items: center;
    gap: 1.5rem;
    font-size: 2.2rem;
    font-weight: 700;
    color: #2d3748;
    margin-bottom: 3rem;
    padding-bottom: 1.5rem;
    border-bottom: 3px solid transparent;
    background: linear-gradient(90deg, #e2e8f0 0%, transparent 100%) bottom/100% 3px no-repeat;
    position: relative;
}

.category-title::before {
    content: '';
    position: absolute;
    bottom: -3px;
    left: 0;
    width: 100px;
    height: 3px;
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    border-radius: 2px;
}

.category-title i {
    color: #667eea;
    font-size: 2rem;
    background: rgba(102, 126, 234, 0.1);
    padding: 1rem;
    border-radius: 16px;
    transition: all 0.3s ease;
}

.category-title:hover i {
    transform: scale(1.1) rotate(5deg);
    background: rgba(102, 126, 234, 0.2);
}

/* Subjects Grid */
.subjects-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(380px, 1fr));
    gap: 2.5rem;
}

.subject-card {
    background: rgba(255, 255, 255, 0.9);
    backdrop-filter: blur(20px);
    border-radius: 20px;
    padding: 2rem;
    box-shadow: 0 10px 40px rgba(0, 0, 0, 0.08);
    border: 1px solid rgba(255, 255, 255, 0.3);
    transition: all 0.4s cubic-bezier(0.4, 0, 0.2, 1);
    position: relative;
    overflow: hidden;
}

.subject-card::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    height: 4px;
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    transform: scaleX(0);
    transition: transform 0.4s cubic-bezier(0.4, 0, 0.2, 1);
}

.subject-card:hover {
    transform: translateY(-8px);
    box-shadow: 0 25px 60px rgba(0, 0, 0, 0.15);
    border-color: rgba(102, 126, 234, 0.3);
}

.subject-card:hover::before {
    transform: scaleX(1);
}

.subject-header {
    display: flex;
    align-items: center;
    gap: 1.5rem;
    margin-bottom: 2rem;
    padding-bottom: 1.5rem;
    border-bottom: 2px solid #f7fafc;
}

.subject-header i {
    font-size: 1.8rem;
    color: #667eea;
    background: linear-gradient(135deg, rgba(102, 126, 234, 0.1) 0%, rgba(118, 75, 162, 0.1) 100%);
    padding: 1rem;
    border-radius: 16px;
    transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
}

.subject-header:hover i {
    transform: scale(1.1);
    background: linear-gradient(135deg, rgba(102, 126, 234, 0.2) 0%, rgba(118, 75, 162, 0.2) 100%);
}

.subject-header h4 {
    font-size: 1.5rem;
    font-weight: 700;
    color: #2d3748;
    transition: color 0.3s ease;
}

.subject-card:hover .subject-header h4 {
    color: #667eea;
}

/* Papers List */
.papers-list {
    display: flex;
    flex-direction: column;
    gap: 1rem;
}

.paper-item {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 1rem 1.5rem;
    background: linear-gradient(135deg, #f8fafc 0%, #edf2f7 100%);
    border-radius: 12px;
    transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
    border: 1px solid transparent;
    position: relative;
    overflow: hidden;
}

.paper-item::before {
    content: '';
    position: absolute;
    top: 0;
    left: -100%;
    width: 100%;
    height: 100%;
    background: linear-gradient(135deg, rgba(102, 126, 234, 0.05) 0%, rgba(118, 75, 162, 0.05) 100%);
    transition: left 0.3s cubic-bezier(0.4, 0, 0.2, 1);
    z-index: 0;
}

.paper-item:hover {
    transform: translateX(5px);
    border-color: rgba(102, 126, 234, 0.2);
    box-shadow: 0 5px 20px rgba(102, 126, 234, 0.1);
}

.paper-item:hover::before {
    left: 0;
}

.year {
    font-weight: 700;
    color: #4a5568;
    font-size: 1.1rem;
    position: relative;
    z-index: 1;
    transition: color 0.3s ease;
}

.paper-item:hover .year {
    color: #667eea;
}

.download-btn {
    display: flex;
    align-items: center;
    gap: 0.6rem;
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    color: white;
    border: none;
    padding: 0.8rem 1.5rem;
    border-radius: 10px;
    font-weight: 600;
    font-size: 0.95rem;
    cursor: pointer;
    transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
    position: relative;
    z-index: 1;
    overflow: hidden;
}

.download-btn::before {
    content: '';
    position: absolute;
    top: 0;
    left: -100%;
    width: 100%;
    height: 100%;
    background: linear-gradient(135deg, #5a67d8 0%, #6b46c1 100%);
    transition: left 0.3s cubic-bezier(0.4, 0, 0.2, 1);
    z-index: -1;
}

.download-btn:hover {
    transform: translateY(-2px);
    box-shadow: 0 8px 25px rgba(102, 126, 234, 0.4);
}

.download-btn:hover::before {
    left: 0;
}

.download-btn:active {
    transform: translateY(0);
}

.download-btn i {
    font-size: 0.9rem;
    transition: transform 0.3s ease;
}

.download-btn:hover i {
    transform: translateY(-1px);
}

/* Search Container */
.search-container {
    max-width: 500px;
    margin: 0 auto 3rem;
    position: relative;
}

.search-box {
    position: relative;
    display: flex;
    align-items: center;
}

.search-box i {
    position: absolute;
    left: 1.5rem;
    color: #a0aec0;
    z-index: 1;
    font-size: 1.1rem;
    transition: color 0.3s ease;
}

.search-box input {
    width: 100%;
    padding: 1.2rem 1.5rem 1.2rem 3.5rem;
    border: 2px solid rgba(102, 126, 234, 0.2);
    border-radius: 60px;
    font-size: 1.1rem;
    background: rgba(255, 255, 255, 0.9);
    backdrop-filter: blur(10px);
    transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
    font-weight: 500;
}

.search-box input:focus {
    outline: none;
    border-color: #667eea;
    box-shadow: 0 0 0 4px rgba(102, 126, 234, 0.1);
    background: rgba(255, 255, 255, 1);
}

.search-box input:focus + i {
    color: #667eea;
}

/* Footer */
.footer {
    background: linear-gradient(135deg, #2d3748 0%, #1a202c 100%);
    color: #a0aec0;
    padding: 80px 0 30px;
    position: relative;
    overflow: hidden;
}

.footer::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    height: 1px;
    background: linear-gradient(90deg, transparent 0%, #667eea 50%, transparent 100%);
}

.footer-content {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
    gap: 4rem;
    margin-bottom: 3rem;
}

.footer-section h4 {
    color: #fff;
    font-size: 1.4rem;
    font-weight: 700;
    margin-bottom: 1.5rem;
    position: relative;
}

.footer-section h4::after {
    content: '';
    position: absolute;
    bottom: -8px;
    left: 0;
    width: 40px;
    height: 3px;
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    border-radius: 2px;
}

.footer-section p {
    line-height: 1.8;
    font-size: 1.05rem;
}

.footer-section ul {
    list-style: none;
}

.footer-section ul li {
    margin-bottom: 0.8rem;
}

.footer-section ul li a {
    color: #a0aec0;
    text-decoration: none;
    transition: all 0.3s ease;
    font-weight: 500;
    position: relative;
}

.footer-section ul li a::before {
    content: '';
    position: absolute;
    bottom: -2px;
    left: 0;
    width: 0;
    height: 2px;
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    transition: width 0.3s ease;
}

.footer-section ul li a:hover {
    color: #667eea;
    transform: translateX(5px);
}

.footer-section ul li a:hover::before {
    width: 100%;
}

.footer-bottom {
    text-align: center;
    padding-top: 2.5rem;
    border-top: 1px solid #4a5568;
    font-size: 1.05rem;
}

/* Animations */
@keyframes fadeInUp {
    from {
        opacity: 0;
        transform: translateY(30px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

@keyframes pulse {
    0%, 100% {
        transform: scale(1);
    }
    50% {
        transform: scale(1.05);
    }
}

/* Responsive Design */
@media (max-width: 768px) {
    .hero-title {
        font-size: 2.8rem;
    }
    
    .hero-subtitle {
        font-size: 1.2rem;
    }
    
    .hero-stats {
        gap: 3rem;
    }
    
    .nav {
        gap: 1.5rem;
    }
    
    .subjects-grid {
        grid-template-columns: 1fr;
    }
    
    .filter-tabs {
        gap: 1rem;
    }
    
    .filter-tab {
        padding: 0.8rem 1.5rem;
        font-size: 0.95rem;
    }
    
    .section-title {
        font-size: 2.2rem;
    }
    
    .category-title {
        font-size: 1.8rem;
    }
    
    .subject-card {
        padding: 1.5rem;
    }
}

@media (max-width: 480px) {
    .hero-title {
        font-size: 2.2rem;
    }
    
    .hero-subtitle {
        font-size: 1.1rem;
    }
    
    .hero-stats {
        flex-direction: column;
        gap: 2rem;
    }
    
    .nav {
        flex-direction: column;
        gap: 1rem;
    }
    
    .header-content {
        flex-direction: column;
        gap: 1.5rem;
    }
    
    .hero {
        padding: 120px 0 80px;
    }
    
    .cta-button {
        padding: 1rem 2rem;
        font-size: 1.1rem;
    }
    
    .subjects-grid {
        grid-template-columns: 1fr;
    }
    
    .subject-card {
        margin: 0 10px;
    }
}

/* Animation for smooth scrolling */
html {
    scroll-behavior: smooth;
}

/* Loading animation for download buttons */
.download-btn.loading {
    opacity: 0.8;
    pointer-events: none;
    animation: pulse 1.5s infinite;
}

.download-btn.loading::after {
    content: '';
    width: 14px;
    height: 14px;
    border: 2px solid transparent;
    border-top: 2px solid currentColor;
    border-radius: 50%;
    animation: spin 1s linear infinite;
    margin-left: 0.5rem;
}

@keyframes spin {
    to {
        transform: rotate(360deg);
    }
}

/* Hidden class for filtering */
.hidden {
    display: none !important;
}

/* Notification Styles */
.notification {
    position: fixed;
    top: 120px;
    right: 30px;
    background: rgba(255, 255, 255, 0.95);
    backdrop-filter: blur(20px);
    border-radius: 16px;
    box-shadow: 0 20px 60px rgba(0, 0, 0, 0.15);
    z-index: 1001;
    animation: slideInRight 0.4s cubic-bezier(0.4, 0, 0.2, 1);
    max-width: 420px;
    border: 1px solid rgba(255, 255, 255, 0.3);
}

.notification-success {
    border-left: 4px solid #48bb78;
}

.notification-content {
    display: flex;
    align-items: center;
    gap: 1rem;
    padding: 1.5rem 2rem;
}

.notification-content i:first-child {
    color: #48bb78;
    font-size: 1.4rem;
}

.notification-content span {
    font-weight: 600;
    color: #2d3748;
}

.notification-close {
    background: none;
    border: none;
    color: #a0aec0;
    cursor: pointer;
    padding: 0.5rem;
    margin-left: auto;
    border-radius: 8px;
    transition: all 0.3s ease;
}

.notification-close:hover {
    color: #2d3748;
    background: rgba(160, 174, 192, 0.1);
}

@keyframes slideInRight {
    from {
        transform: translateX(100%);
        opacity: 0;
    }
    to {
        transform: translateX(0);
        opacity: 1;
    }
}

@keyframes slideOutRight {
    from {
        transform: translateX(0);
        opacity: 1;
    }
    to {
        transform: translateX(100%);
        opacity: 0;
    }
}

/* Custom Scrollbar */
::-webkit-scrollbar {
    width: 8px;
}

::-webkit-scrollbar-track {
    background: #f1f5f9;
}

::-webkit-scrollbar-thumb {
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    border-radius: 4px;
}

::-webkit-scrollbar-thumb:hover {
    background: linear-gradient(135deg, #5a67d8 0%, #6b46c1 100%);
}