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

body {
    font-family: 'Avenir LT W01 35 Light 1475496', -apple-system, BlinkMacSystemFont, sans-serif;
    line-height: 1.6;
    color: #333;
    background: linear-gradient(135deg, #f5f7fa 0%, #c3cfe2 100%);
}

.header {
    background: rgba(255, 255, 255, 0.95);
    backdrop-filter: blur(10px);
    position: sticky;
    top: 0;
    z-index: 100;
    padding: 1rem 0;
    box-shadow: 0 2px 20px rgba(0,0,0,0.1);
}

.nav {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 2rem;
}

.nav ul {
    list-style: none;
    display: flex;
    justify-content: center;
    gap: 3rem;
}

.nav-link {
    text-decoration: none;
    color: #333;
    font-weight: 500;
    font-size: 1.1rem;
    padding: 0.5rem 1rem;
    border-radius: 25px;
    transition: all 0.3s ease;
    position: relative;
}

.nav-link.active,
.nav-link:hover {
    background: linear-gradient(45deg, #007bff, #0056b3);
    color: white;
    transform: translateY(-2px);
}

.main {
    max-width: 1200px;
    margin: 0 auto;
    padding: 2rem;
}

.section {
    margin-bottom: 4rem;
}

/* IMAGE SIZING SYSTEM - FROM TEXT SIZE TO FULL SCREEN */
.img-xs { /* Text size - 16px */
    width: 16px;
    height: 16px;
}

.img-sm { /* Icon size - 24px */
    width: 24px;
    height: 24px;
}

.img-md { /* Thumbnail - 48px */
    width: 48px;
    height: 48px;
    border-radius: 8px;
}

.img-lg { /* Profile/small card - 80px */
    width: 80px;
    height: 80px;
    border-radius: 12px;
}

.img-xl { /* Card image - 200px */
    width: 200px;
    height: 200px;
    border-radius: 16px;
}

.img-card { /* Challenge card - 250px height, responsive width */
    width: 100%;
    height: 250px;
    object-fit: cover;
    transition: transform 0.4s ease;
}

.img-wide { /* Wide card - 300px height */
    width: 100%;
    height: 300px;
    object-fit: cover;
}

.img-hero-sm { /* Small hero - 400px height */
    width: 100%;
    height: 400px;
    object-fit: cover;
    border-radius: 20px;
}

.img-hero-md { /* Medium hero - 500px height */
    width: 100%;
    height: 500px;
    object-fit: cover;
    border-radius: 24px;
}

.img-hero-lg { /* Large hero - 600px height */
    width: 100%;
    height: 600px;
    object-fit: cover;
    border-radius: 28px;
}

.img-full { /* Full viewport height */
    width: 100vw;
    height: 100vh;
    object-fit: cover;
    position: relative;
}

.img-fullscreen { /* Full screen with overlay */
    width: 100vw;
    height: 100vh;
    object-fit: cover;
    position: fixed;
    top: 0;
    left: 0;
    z-index: 999;
}

.hero {
    text-align: center;
    padding: 6rem 2rem;
    background: linear-gradient(135deg, rgba(0,123,255,0.1) 0%, rgba(0,86,179,0.1) 100%);
    border-radius: 20px;
    margin-bottom: 6rem;
}

.hero-title {
    font-size: 3.5rem;
    font-weight: 300;
    letter-spacing: 0.05em;
    margin-bottom: 2rem;
    background: linear-gradient(45deg, #007bff, #0056b3);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.hero-line {
    width: 100px;
    height: 3px;
    background: linear-gradient(45deg, #007bff, #0056b3);
    margin: 0 auto;
    border-radius: 2px;
}

.challenges-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(350px, 1fr));
    gap: 2rem;
}

.challenge-card {
    background: white;
    border-radius: 20px;
    overflow: hidden;
    box-shadow: 0 10px 40px rgba(0,0,0,0.1);
    transition: all 0.4s ease;
    position: relative;
}

.challenge-card:hover {
    transform: translateY(-10px);
    box-shadow: 0 20px 60px rgba(0,0,0,0.15);
}

.challenge-card:hover .img-card {
    transform: scale(1.05);
}

.challenge-card h3 {
    font-size: 1.4rem;
    font-weight: 500;
    margin: 1.5rem 1.5rem 0.5rem;
    color: #2c3e50;
}

.challenge-card p {
    font-size: 1rem;
    margin: 0 1.5rem 1.5rem;
    color: #666;
    line-height: 1.7;
}

.footer {
    text-align: center;
    padding: 3rem 2rem;
    color: #666;
    font-size: 0.9rem;
    background: rgba(255,255,255,0.8);
    backdrop-filter: blur(10px);
    border-top: 1px solid rgba(0,0,0,0.1);
}

/* Image hover effects */
.img-hover-scale:hover {
    transform: scale(1.05);
    transition: transform 0.3s ease;
}

.img-hover-zoom:hover {
    transform: scale(1.1);
    transition: transform 0.4s ease;
}

.img-rounded { border-radius: 50%; }
.img-square { border-radius: 8px; }
.img-pill { border-radius: 50px; }

/* Responsive image adjustments */
@media (max-width: 768px) {
    .nav ul {
        gap: 1rem;
        flex-wrap: wrap;
    }
    
    .hero-title {
        font-size: 2.5rem;
    }
    
    .challenges-grid {
        grid-template-columns: 1fr;
        gap: 1.5rem;
    }
    
    .main {
        padding: 1rem;
    }
    
    /* Scale down hero images on mobile */
    .img-hero-lg { height: 400px; }
    .img-hero-md { height: 350px; }
    .img-hero-sm { height: 300px; }
    
    .img-card { height: 200px; }
    .img-wide { height: 250px; }
}

@media (max-width: 480px) {
    .img-hero-lg { height: 300px; }
    .img-hero-md { height: 280px; }
    .img-card { height: 180px; }
}