:root {
    --primary-color: #2563eb;
    --secondary-color: #64748b;
    --background: #f8fafc;
    --card-background: #ffffff;
    --text-primary: #1e293b;
    --text-secondary: #64748b;
    --border-color: #e2e8f0;
    --shadow: 0 1px 3px rgba(0, 0, 0, 0.1);
    --shadow-lg: 0 10px 25px rgba(0, 0, 0, 0.1);
}

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

body {
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
    line-height: 1.6;
    color: var(--text-primary);
    background: var(--background);
}

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

/* Header */
.header {
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    color: white;
    padding: 60px 20px;
    text-align: center;
    box-shadow: var(--shadow-lg);
}

.header-title {
    font-size: 3rem;
    margin-bottom: 10px;
    font-weight: 700;
}

.header-subtitle {
    font-size: 1.2rem;
    opacity: 0.9;
}

/* Stats */
.stats {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
    gap: 20px;
    margin: 40px 0;
}

.stat-card {
    background: var(--card-background);
    padding: 30px;
    border-radius: 12px;
    text-align: center;
    box-shadow: var(--shadow);
    transition: transform 0.2s;
}

.stat-card:hover {
    transform: translateY(-5px);
    box-shadow: var(--shadow-lg);
}

.stat-number {
    font-size: 2.5rem;
    font-weight: 700;
    color: var(--primary-color);
    margin-bottom: 5px;
}

.stat-label {
    color: var(--text-secondary);
    font-size: 0.9rem;
}

/* Controls */
.controls {
    margin-bottom: 40px;
}

.search-box {
    margin-bottom: 20px;
}

.search-input {
    width: 100%;
    padding: 15px 20px;
    font-size: 1rem;
    border: 2px solid var(--border-color);
    border-radius: 10px;
    background: var(--card-background);
    transition: border-color 0.3s;
}

.search-input:focus {
    outline: none;
    border-color: var(--primary-color);
}

.filters {
    display: flex;
    gap: 15px;
    flex-wrap: wrap;
}

.filter-select {
    flex: 1;
    min-width: 150px;
    padding: 12px 15px;
    font-size: 0.95rem;
    border: 2px solid var(--border-color);
    border-radius: 10px;
    background: var(--card-background);
    cursor: pointer;
    transition: border-color 0.3s;
}

.filter-select:focus {
    outline: none;
    border-color: var(--primary-color);
}

/* Projects Grid */
.projects {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(350px, 1fr));
    gap: 30px;
    margin-bottom: 60px;
}

.project-card {
    background: var(--card-background);
    border-radius: 12px;
    padding: 25px;
    box-shadow: var(--shadow);
    transition: transform 0.2s, box-shadow 0.2s;
    border: 2px solid transparent;
}

.project-card:hover {
    transform: translateY(-5px);
    box-shadow: var(--shadow-lg);
    border-color: var(--primary-color);
}

.project-number {
    display: inline-block;
    background: var(--primary-color);
    color: white;
    padding: 5px 12px;
    border-radius: 20px;
    font-size: 0.85rem;
    font-weight: 600;
    margin-bottom: 15px;
}

.project-title {
    font-size: 1.4rem;
    font-weight: 700;
    margin-bottom: 8px;
    color: var(--text-primary);
}

.project-subtitle {
    color: var(--text-secondary);
    font-size: 0.95rem;
    margin-bottom: 15px;
}

.project-description {
    color: var(--text-secondary);
    font-size: 0.9rem;
    line-height: 1.5;
    margin-bottom: 15px;
}

.project-meta {
    display: flex;
    gap: 15px;
    margin-bottom: 15px;
    font-size: 0.85rem;
    color: var(--text-secondary);
}

.difficulty-badge {
    display: inline-block;
    padding: 4px 10px;
    border-radius: 15px;
    font-size: 0.8rem;
    font-weight: 600;
}

.difficulty-1 { background: #dbeafe; color: #1e40af; }
.difficulty-2 { background: #d1fae5; color: #065f46; }
.difficulty-3 { background: #fef3c7; color: #92400e; }
.difficulty-4 { background: #fed7aa; color: #9a3412; }
.difficulty-5 { background: #fecaca; color: #991b1b; }

.project-tags {
    display: flex;
    flex-wrap: wrap;
    gap: 8px;
    margin-bottom: 15px;
}

.tag {
    background: var(--background);
    color: var(--text-secondary);
    padding: 4px 10px;
    border-radius: 15px;
    font-size: 0.8rem;
}

.project-links {
    display: flex;
    gap: 10px;
}

.btn {
    flex: 1;
    padding: 10px 15px;
    border: none;
    border-radius: 8px;
    font-size: 0.9rem;
    font-weight: 600;
    cursor: pointer;
    text-align: center;
    text-decoration: none;
    transition: background 0.2s;
}

.btn-primary {
    background: var(--primary-color);
    color: white;
}

.btn-primary:hover {
    background: #1d4ed8;
}

.btn-secondary {
    background: var(--background);
    color: var(--text-primary);
}

.btn-secondary:hover {
    background: var(--border-color);
}

/* Loading & Empty */
.loading, .empty-state {
    text-align: center;
    padding: 60px 20px;
    color: var(--text-secondary);
    font-size: 1.1rem;
}

/* Footer */
.footer {
    background: var(--card-background);
    padding: 30px 20px;
    text-align: center;
    color: var(--text-secondary);
    border-top: 1px solid var(--border-color);
    margin-top: 60px;
}

.footer-updated {
    margin-top: 10px;
    font-size: 0.9rem;
}

/* Responsive */
@media (max-width: 768px) {
    .header-title {
        font-size: 2rem;
    }

    .projects {
        grid-template-columns: 1fr;
    }

    .filters {
        flex-direction: column;
    }
}