/* === INTRO SECTION === */
.intro-section {
    background: transparent;
    backdrop-filter: blur(20px);
    border: var(--border-1) solid var(--glass-border);
    border-radius: var(--radius-2xl);
    padding: var(--space-3xl);
    box-shadow: var(--shadow-light);
    text-align: center;
    position: relative;
    overflow: hidden;
}

.intro-section h1 {
    font-size: clamp(var(--font-size-3xl), 5vw, var(--font-size-6xl));
    font-weight: 300;
    line-height: var(--space-2xl);
    margin-bottom: var(--space-sm);
    background: var(--gradient-primary-secondary);
    background-clip: text;
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    text-shadow: 0 0 30px var(--primary-opacity-50);
    animation: glow 3s ease-in-out infinite alternate;
}

.intro-text {
    font-size: clamp(var(--font-size-lg), 3vw, var(--font-size-2xl));
    color: var(--text-secondary);
    line-height: var(--line-height-loose);
    margin-bottom: var(--space-xl);
}

.warning-box {
    background: var(--secondary-opacity-10);
    border: var(--border-2) solid var(--secondary-opacity-20);
    border-radius: var(--radius-lg);
    padding: var(--space-lg);
    color: var(--text-secondary);
    font-size: var(--font-size-base);
    margin-top: var(--space-lg);
}

.intro-section::after {
    content: '';
    position: absolute;
    top: -50%;
    left: -50%;
    width: 200%;
    height: 200%;
    background: 
        radial-gradient(circle, var(--secondary) 1px, transparent 1px);
    background-size: 50px 50px;
    animation: moveStars 20s linear infinite;
    z-index: -1;
}

@keyframes moveStars {
    0% { transform: translate(0, 0); }
    100% { transform: translate(-50px, -50px); }
}

/* === DOWNLOAD FULL === */
.download-full-section {
    background: var(--glass-bg);
    backdrop-filter: blur(20px);
    border: var(--border-1) solid var(--glass-border);
    border-radius: var(--radius-2xl);
    padding: var(--space-xl);
    box-shadow: var(--shadow-light);
    text-align: center;
}

.download-full-section h2 {
    color: var(--text-primary); 
    margin-bottom: var(--space-lg); 
    font-weight: var(--font-weight-light);
}

.download-full-link {
    position: relative;
    overflow: hidden;
    display: inline-flex;
    align-items: center;
    gap: var(--space-md);
    background: transparent;
    color: var(--text-primary);
    text-decoration: none;
    padding: var(--space-lg) var(--space-3xl);
    border-radius: var(--radius-xl);
    border: var(--border-2) solid var(--secondary);
    font-size: var(--font-size-xl);
    font-weight: var(--font-weight-semibold);
    box-shadow: var(--shadow-secondary);
    transition: var(--transition);
}

.download-full-link::before {
    content: "";
    position: absolute;
    inset: 0;
    transform: translateX(-100%);
    transition: var(--transition);
    z-index: -1;
    background: var(--gradient-secondary);
}

.download-full-link:hover::before {
    transform: translateX(0);
}

.download-full-link:hover {
    transform: translateY(-3px);
    box-shadow: 0 15px 35px var(--secondary-opacity-20);
}

.download-full-link img {
    width: 30px;
    height: auto;
}

.download-full-link svg {
    width: 24px;
    height: auto;
    fill: var(--secondary-dark);
    transition: var(--transition);
}

.download-full-link:hover svg {
    fill: var(--secondary);
    transform: translateX(5px);
}

/* === MATHEMATICS SECTION === */
.mathematics-section {
    background: 
        radial-gradient(circle at 80% 20%, var(--primary-opacity-10) 0%, transparent 50%),
        radial-gradient(circle at 20% 80%, var(--secondary-opacity-10) 0%, transparent 50%);
    backdrop-filter: blur(20px);
    border: var(--border-1) solid var(--glass-border);
    border-radius: var(--radius-2xl);
    padding: var(--space-3xl);
    box-shadow: var(--shadow-light);
    position: relative;
    overflow: hidden;
}

.section-title {
    font-size: var(--font-size-3xl);
    font-weight: var(--font-weight-bold);
    color: var(--text-primary);
    text-align: center;
    margin-bottom: var(--space-xl);
    position: relative;
}

.section-title::after {
    content: '';
    position: absolute;
    bottom: -10px;
    left: 50%;
    transform: translateX(-50%);
    width: 180px;
    height: var(--border-4);
    background: var(--gradient-primary-secondary);
    border-radius: var(--radius-xl);
}

.physics-section .section-title::after {
    background: linear-gradient(135deg, var(--tertiary), var(--quaternary));
}

/* === YEAR SECTIONS === */
.year-section {
    margin-bottom: var(--space-2xl);
}

.year-title {
    display: flex;
    align-items: center;
    gap: var(--space-md);
    margin-bottom: var(--space-lg);
}

.year-badge {
    background: var(--gradient-primary-secondary);
    color: var(--text-primary);
    padding: var(--space-sm) var(--space-lg);
    border-radius: var(--radius-xl);
    font-size: var(--font-size-lg);
    font-weight: var(--font-weight-semibold);
    box-shadow: var(--shadow-primary);
}

.year-text {
    font-size: var(--font-size-2xl);
    font-weight: var(--font-weight-bold);
    color: var(--text-primary);
}

/* === PDF LINKS GRID === */
.pdf-links {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: var(--space-md);
}

.pdf-link {
    display: flex;
    align-items: center;
    gap: var(--space-md);
    background: var(--bg-card);
    color: var(--text-secondary);
    text-decoration: none;
    padding: var(--space-lg);
    border-radius: var(--radius-lg);
    border: var(--border-1) solid var(--glass-border);
    transition: var(--transition);
    position: relative;
    overflow: hidden;
}

.pdf-link::before {
    content: '';
    position: absolute;
    top: 0;
    left: -100%;
    width: 100%;
    height: 100%;
    background: linear-gradient(90deg, transparent, var(--primary-opacity-10), transparent);
    transition: left 0.5s ease;
}

.level-section .pdf-link::before {
    background: linear-gradient(90deg, transparent, var(--tertiary-opacity-10), transparent);
}

.pdf-link:hover::before {
    left: 100%;
}

.pdf-link:hover {
    background: var(--bg-card-hover);
    color: var(--text-primary);
    transform: translateY(-2px);
    box-shadow: var(--shadow-card);
    border-color: var(--primary-opacity-20);
}

.level-section .pdf-link:hover {
    border-color: var(--tertiary-opacity-20);
}

.pdf-link img {
    width: 30px;
    height: auto;
}

.pdf-icon {
    width: 30px;
    height: auto;
}

.pdf-text {
    font-size: var(--font-size-lg);
    font-weight: var(--font-weight-medium);
    flex-grow: 1;
}

.pdf-link svg {
    width: 24px;
    height: auto;
    flex-shrink: 0;
    fill: var(--primary-dark);
    transition: var(--transition);
}

.pdf-link:hover svg {
    fill: var(--primary);
    transform: translateX(5px);
}

.level-section .pdf-link svg {
    fill: var(--tertiary-dark);
}

.level-section .pdf-link:hover svg {
    fill: var(--tertiary);
}

/* === PHYSICS SECTION === */
.physics-section {
    background: 
        radial-gradient(circle at 25% 25%, var(--tertiary-opacity-10) 0%, transparent 60%),
        radial-gradient(circle at 75% 75%, var(--quaternary-opacity-10) 0%, transparent 60%);
    backdrop-filter: blur(20px);
    border: var(--border-1) solid var(--glass-border);
    border-radius: var(--radius-2xl);
    padding: var(--space-3xl);
    box-shadow: var(--shadow-light);
    position: relative;
    overflow: hidden;
}

.level-section {
    margin-bottom: var(--space-xl);
}

.level-title {
    display: flex;
    align-items: center;
    gap: var(--space-md);
    margin-bottom: var(--space-lg);
}

.level-badge {
    background: linear-gradient(135deg, var(--tertiary), var(--quaternary));
    color: var(--text-primary);
    padding: var(--space-sm) var(--space-lg);
    border-radius: var(--radius-xl);
    font-size: var(--font-size-base);
    font-weight: var(--font-weight-semibold);
    box-shadow: var(--shadow-tertiary);
}

.level-text {
    font-size: var(--font-size-xl);
    font-weight: var(--font-weight-semibold);
    color: var(--text-primary);
}

/* === RESPONSIVE === */
@media (max-width: 768px) {
    .intro-section,
    .mathematics-section,
    .physics-section {
        padding: var(--space-xl);
    }

    .pdf-links {
        grid-template-columns: 1fr;
    }

    .year-title,
    .level-title {
        flex-direction: column;
        align-items: flex-start;
        gap: var(--space-sm);
    }
}

@media (max-width: 480px) {
    .intro-section,
    .mathematics-section,
    .physics-section {
        padding: var(--space-lg);
    }

    .download-full-link {
        gap: var(--space-sm);
        padding: var(--space-sm) var(--space-md);
        font-size: var(--font-size-md);
    }

    .pdf-text {
        font-size: var(--font-size-md);
    }

    .download-full-link svg,
    .pdf-link svg {
        width: 16px;
        height: auto;
    }

    .download-full-link img,
    .pdf-link img {
        width: 22px;
        height: auto;
    }

    .intro-section h1 {
        font-size: var(--font-size-3xl);
    }
}

/* === ANIMACIONS === */
.intro-section { animation: slideInUp 0.8s ease-out; }
.download-full-section { animation: slideInUp 1s ease-out 0.2s both; }
.mathematics-section { animation: slideInUp 1s ease-out 0.4s both; }
.physics-section { animation: slideInUp 1s ease-out 0.6s both; }

@keyframes slideInUp {
    from {
        opacity: 0;
        transform: translateY(30px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}