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

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, sans-serif;
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    min-height: 100vh;
    padding: 20px;
}

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

header {
    text-align: center;
    color: white;
    margin-bottom: 40px;
    padding: 40px 0;
}

header h1 {
    font-size: 2.5rem;
    margin-bottom: 10px;
    text-shadow: 2px 2px 4px rgba(0, 0, 0, 0.2);
}

header p {
    font-size: 1.1rem;
    opacity: 0.9;
}

.search-section {
    background: white;
    border-radius: 16px;
    padding: 30px;
    margin-bottom: 30px;
    box-shadow: 0 10px 40px rgba(0, 0, 0, 0.2);
    display: flex;
    flex-wrap: wrap;
    gap: 20px;
    align-items: center;
}

.keywords-input {
    flex: 1;
    min-width: 300px;
}

.keywords-input label {
    display: block;
    font-weight: 600;
    color: #333;
    margin-bottom: 10px;
}

#keywords-container {
    display: flex;
    flex-wrap: wrap;
    gap: 8px;
}

.keyword-tag {
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    color: white;
    padding: 8px 16px;
    border-radius: 20px;
    font-size: 0.9rem;
}

.btn-primary, .btn-secondary {
    padding: 14px 28px;
    border: none;
    border-radius: 10px;
    font-size: 1rem;
    font-weight: 600;
    cursor: pointer;
    transition: all 0.3s ease;
}

.btn-primary {
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    color: white;
}

.btn-primary:hover {
    transform: translateY(-2px);
    box-shadow: 0 6px 20px rgba(102, 126, 234, 0.4);
}

.btn-secondary {
    background: #f0f0f0;
    color: #333;
}

.btn-secondary:hover {
    background: #e0e0e0;
}

.loading {
    text-align: center;
    padding: 60px;
    color: white;
}

.spinner {
    width: 50px;
    height: 50px;
    border: 4px solid rgba(255, 255, 255, 0.3);
    border-top-color: white;
    border-radius: 50%;
    animation: spin 1s linear infinite;
    margin: 0 auto 20px;
}

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

.papers-list {
    display: grid;
    gap: 20px;
}

.paper-card {
    background: white;
    border-radius: 16px;
    padding: 25px;
    box-shadow: 0 4px 20px rgba(0, 0, 0, 0.1);
    cursor: pointer;
    transition: all 0.3s ease;
}

.paper-card:hover {
    transform: translateY(-4px);
    box-shadow: 0 8px 30px rgba(0, 0, 0, 0.15);
}

.paper-card h3 {
    color: #333;
    font-size: 1.2rem;
    margin-bottom: 12px;
    line-height: 1.4;
}

.paper-meta {
    display: flex;
    flex-wrap: wrap;
    gap: 15px;
    color: #666;
    font-size: 0.9rem;
    margin-bottom: 12px;
}

.paper-meta span {
    display: flex;
    align-items: center;
    gap: 5px;
}

.paper-authors {
    color: #888;
    font-size: 0.9rem;
    margin-bottom: 12px;
}

.paper-abstract {
    color: #555;
    font-size: 0.95rem;
    line-height: 1.6;
    display: -webkit-box;
    -webkit-line-clamp: 3;
    -webkit-box-orient: vertical;
    overflow: hidden;
}

.paper-categories {
    display: flex;
    flex-wrap: wrap;
    gap: 8px;
    margin-top: 15px;
}

.category-tag {
    background: #f0f0f0;
    color: #666;
    padding: 4px 12px;
    border-radius: 12px;
    font-size: 0.8rem;
}

.modal {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: rgba(0, 0, 0, 0.6);
    display: flex;
    align-items: center;
    justify-content: center;
    z-index: 1000;
    padding: 20px;
}

.modal.hidden {
    display: none;
}

.modal-content {
    background: white;
    border-radius: 20px;
    max-width: 900px;
    width: 100%;
    max-height: 90vh;
    overflow-y: auto;
    position: relative;
}

.modal-header {
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    color: white;
    padding: 30px;
    border-radius: 20px 20px 0 0;
    position: sticky;
    top: 0;
}

.modal-header h2 {
    font-size: 1.4rem;
    line-height: 1.4;
    padding-right: 40px;
}

.close-btn {
    position: absolute;
    top: 20px;
    right: 20px;
    background: rgba(255, 255, 255, 0.2);
    border: none;
    color: white;
    font-size: 2rem;
    width: 40px;
    height: 40px;
    border-radius: 50%;
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: background 0.3s ease;
}

.close-btn:hover {
    background: rgba(255, 255, 255, 0.3);
}

.modal-body {
    padding: 30px;
}

.analysis-section {
    margin-bottom: 30px;
}

.analysis-section h3 {
    color: #667eea;
    font-size: 1.1rem;
    margin-bottom: 12px;
    display: flex;
    align-items: center;
    gap: 10px;
}

.analysis-section h3::before {
    content: '';
    width: 4px;
    height: 20px;
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    border-radius: 2px;
}

.analysis-section p, .analysis-section ul {
    color: #444;
    line-height: 1.8;
}

.analysis-section ul {
    margin-left: 20px;
}

.analysis-section li {
    margin-bottom: 8px;
}

.info-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: 20px;
    margin-bottom: 30px;
}

.info-box {
    background: #f8f9fa;
    border-radius: 12px;
    padding: 20px;
}

.info-box h4 {
    color: #666;
    font-size: 0.9rem;
    margin-bottom: 8px;
    text-transform: uppercase;
    letter-spacing: 0.5px;
}

.info-box p {
    color: #333;
    font-size: 1rem;
    font-weight: 500;
}

.hidden {
    display: none !important;
}

.empty-state {
    text-align: center;
    padding: 80px 40px;
    color: white;
}

.empty-state h2 {
    font-size: 1.8rem;
    margin-bottom: 15px;
}

.empty-state p {
    font-size: 1.1rem;
    opacity: 0.9;
}