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

:root {
    --primary-color: #2563eb;
    --secondary-color: #1e40af;
    --accent-color: #3b82f6;
    --text-dark: #1f2937;
    --text-light: #6b7280;
    --bg-light: #f9fafb;
    --bg-white: #ffffff;
    --border-color: #e5e7eb;
    --shadow: 0 4px 6px -1px rgba(0, 0, 0, 0.1), 0 2px 4px -1px rgba(0, 0, 0, 0.06);
    --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1), 0 4px 6px -2px rgba(0, 0, 0, 0.05);
}

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'Helvetica Neue', Arial, sans-serif;
    line-height: 1.6;
    color: var(--text-dark);
    background-color: var(--bg-white);
    overflow-x: hidden;
}

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

/* Navigation */
.navbar {
    background: linear-gradient(135deg, var(--primary-color) 0%, var(--secondary-color) 100%);
    color: white;
    padding: 0.875rem 0;
    position: sticky;
    top: 0;
    z-index: 1000;
    box-shadow: 0 2px 8px rgba(0, 0, 0, 0.1);
}

.nav-container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 20px;
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.logo {
    font-size: 1.25rem;
    font-weight: 700;
}

.nav-menu {
    display: flex;
    list-style: none;
    gap: 1.5rem;
}

.nav-menu a {
    color: white;
    text-decoration: none;
    font-weight: 500;
    font-size: 0.938rem;
    transition: opacity 0.2s;
}

.nav-menu a:hover {
    opacity: 0.85;
}

/* Hero Section */
.hero {
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    color: white;
    padding: 80px 20px;
    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 1440 320"><path fill="%23ffffff" fill-opacity="0.1" d="M0,96L48,112C96,128,192,160,288,160C384,160,480,128,576,122.7C672,117,768,139,864,154.7C960,171,1056,181,1152,165.3C1248,149,1344,107,1392,85.3L1440,64L1440,320L1392,320C1344,320,1248,320,1152,320C1056,320,960,320,864,320C768,320,672,320,576,320C480,320,384,320,288,320C192,320,96,320,48,320L0,320Z"></path></svg>') no-repeat bottom;
    background-size: cover;
    opacity: 0.3;
}

.hero-content {
    position: relative;
    z-index: 1;
    max-width: 800px;
    margin: 0 auto;
}

.hero h1 {
    font-size: 2.5rem;
    margin-bottom: 0.75rem;
    font-weight: 700;
    animation: fadeInUp 0.8s ease-out;
    letter-spacing: -0.02em;
}

.hero p {
    font-size: 1.125rem;
    margin-bottom: 1.75rem;
    opacity: 0.95;
    animation: fadeInUp 0.8s ease-out 0.2s both;
    font-weight: 400;
}

.cta-button {
    background: white;
    color: var(--primary-color);
    border: none;
    padding: 12px 32px;
    font-size: 0.938rem;
    font-weight: 600;
    border-radius: 6px;
    cursor: pointer;
    transition: transform 0.2s, box-shadow 0.2s;
    animation: fadeInUp 0.8s ease-out 0.4s both;
    box-shadow: 0 2px 4px rgba(0, 0, 0, 0.1);
}

.cta-button:hover {
    transform: translateY(-1px);
    box-shadow: 0 4px 8px rgba(0, 0, 0, 0.15);
}

/* Section Styles */
section {
    padding: 60px 0;
}

.section-title {
    font-size: 2rem;
    text-align: center;
    margin-bottom: 2.5rem;
    color: var(--text-dark);
    position: relative;
    padding-bottom: 0.75rem;
    font-weight: 700;
    letter-spacing: -0.01em;
}

.section-title::after {
    content: '';
    position: absolute;
    bottom: 0;
    left: 50%;
    transform: translateX(-50%);
    width: 60px;
    height: 3px;
    background: linear-gradient(90deg, var(--primary-color), var(--accent-color));
    border-radius: 2px;
}

/* Protocols Section */
.protocols-section {
    background-color: var(--bg-light);
}

.protocols-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(240px, 1fr));
    gap: 1.25rem;
}

.protocol-card {
    background: white;
    padding: 1.25rem;
    border-radius: 8px;
    box-shadow: 0 2px 4px rgba(0, 0, 0, 0.08);
    transition: transform 0.2s, box-shadow 0.2s;
    border: 1px solid var(--border-color);
    border-top: 2px solid var(--primary-color);
}

.protocol-card:hover {
    transform: translateY(-2px);
    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.12);
    border-color: var(--primary-color);
    border-top-color: var(--primary-color);
}

.protocol-icon {
    font-size: 2rem;
    margin-bottom: 0.75rem;
    line-height: 1;
}

.protocol-card h3 {
    font-size: 1.125rem;
    color: var(--text-dark);
    margin-bottom: 0.375rem;
    font-weight: 600;
    letter-spacing: -0.01em;
}

.protocol-subtitle {
    color: var(--text-light);
    font-size: 0.813rem;
    margin-bottom: 0.75rem;
    font-weight: 500;
    line-height: 1.4;
}

.protocol-description {
    color: var(--text-light);
    margin-bottom: 1rem;
    line-height: 1.6;
    font-size: 0.875rem;
}

.protocol-details {
    display: flex;
    flex-wrap: wrap;
    gap: 0.375rem;
}

.tag {
    background: var(--bg-light);
    color: var(--primary-color);
    padding: 0.2rem 0.625rem;
    border-radius: 12px;
    font-size: 0.75rem;
    font-weight: 500;
    border: 1px solid rgba(37, 99, 235, 0.1);
}

/* OSI Model Section */
.layers-section {
    background: white;
}

.osi-model {
    max-width: 700px;
    margin: 0 auto;
}

.osi-layer {
    display: flex;
    align-items: center;
    background: linear-gradient(135deg, var(--primary-color), var(--accent-color));
    color: white;
    padding: 1rem 1.5rem;
    margin-bottom: 0.75rem;
    border-radius: 6px;
    box-shadow: 0 2px 4px rgba(0, 0, 0, 0.1);
    transition: transform 0.2s, box-shadow 0.2s;
    cursor: pointer;
}

.osi-layer:hover {
    transform: translateX(5px);
    box-shadow: 0 4px 8px rgba(0, 0, 0, 0.15);
}

.layer-number {
    font-size: 1.5rem;
    font-weight: 700;
    width: 48px;
    height: 48px;
    display: flex;
    align-items: center;
    justify-content: center;
    background: rgba(255, 255, 255, 0.2);
    border-radius: 50%;
    margin-right: 1.25rem;
    flex-shrink: 0;
}

.layer-info h4 {
    font-size: 1.063rem;
    margin-bottom: 0.375rem;
    font-weight: 600;
}

.layer-info p {
    opacity: 0.9;
    font-size: 0.875rem;
    line-height: 1.5;
}

/* History Section */
.history-section {
    background-color: var(--bg-light);
}

.timeline {
    max-width: 800px;
    margin: 0 auto;
    position: relative;
    padding-left: 1.75rem;
}

.timeline::before {
    content: '';
    position: absolute;
    left: 0;
    top: 0;
    bottom: 0;
    width: 4px;
    background: linear-gradient(180deg, var(--primary-color), var(--accent-color));
    border-radius: 2px;
}

.timeline-item {
    display: flex;
    gap: 1.5rem;
    margin-bottom: 2rem;
    position: relative;
    animation: fadeInLeft 0.6s ease-out;
}

.timeline-item::before {
    content: '';
    position: absolute;
    left: -2.25rem;
    top: 0.5rem;
    width: 12px;
    height: 12px;
    background: var(--primary-color);
    border: 3px solid white;
    border-radius: 50%;
    box-shadow: 0 2px 4px rgba(0, 0, 0, 0.1);
}

.timeline-year {
    font-size: 1.125rem;
    font-weight: 700;
    color: var(--primary-color);
    min-width: 70px;
    flex-shrink: 0;
}

.timeline-content {
    background: white;
    padding: 1.25rem;
    border-radius: 6px;
    box-shadow: 0 2px 4px rgba(0, 0, 0, 0.08);
    flex: 1;
    border: 1px solid var(--border-color);
}

.timeline-content h3 {
    margin-bottom: 0.5rem;
    color: var(--text-dark);
    font-size: 1.125rem;
    font-weight: 600;
}

.timeline-content p {
    color: var(--text-light);
    line-height: 1.6;
    font-size: 0.875rem;
}

/* Facts Section */
.facts-section {
    background: white;
}

.facts-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(240px, 1fr));
    gap: 1.25rem;
}

.fact-card {
    background: white;
    padding: 1.25rem;
    border-radius: 8px;
    text-align: center;
    border: 1px solid var(--border-color);
    transition: transform 0.2s, border-color 0.2s, box-shadow 0.2s;
    box-shadow: 0 2px 4px rgba(0, 0, 0, 0.08);
}

.fact-card:hover {
    transform: translateY(-2px);
    border-color: var(--primary-color);
    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.12);
}

.fact-card h3 {
    font-size: 1.063rem;
    margin-bottom: 0.75rem;
    color: var(--text-dark);
    font-weight: 600;
}

.fact-card p {
    color: var(--text-light);
    line-height: 1.6;
    font-size: 0.875rem;
}

/* Footer */
footer {
    background: var(--text-dark);
    color: white;
    padding: 1.5rem 0;
    text-align: center;
}

footer p {
    opacity: 0.8;
    font-size: 0.875rem;
}

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

@keyframes fadeInLeft {
    from {
        opacity: 0;
        transform: translateX(-30px);
    }
    to {
        opacity: 1;
        transform: translateX(0);
    }
}

/* Responsive Design */
@media (max-width: 768px) {
    .nav-menu {
        gap: 1rem;
        font-size: 0.9rem;
    }

    .hero h1 {
        font-size: 2.5rem;
    }

    .hero p {
        font-size: 1.1rem;
    }

    .section-title {
        font-size: 2rem;
    }

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

    .osi-layer {
        flex-direction: column;
        text-align: center;
    }

    .layer-number {
        margin-right: 0;
        margin-bottom: 1rem;
    }

    .timeline-item {
        flex-direction: column;
    }

    .timeline-year {
        min-width: auto;
    }

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

@media (max-width: 480px) {
    .hero {
        padding: 80px 20px;
    }

    .hero h1 {
        font-size: 2rem;
    }

    .nav-menu {
        flex-direction: column;
        gap: 0.5rem;
    }
}