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

html {
    scroll-behavior: smooth;
}

body {
    font-family: 'Open Sans', sans-serif;
    margin: 0;
    padding: 0;
}

/* Kontejner pro omezení šířky obsahu */
.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 50px;
}

/* SEKCE 1: ÚVOD (černé pozadí) */
.intro-wrapper {
    background: #000;
    color: white;
}

/* Navigace */
.top-nav {
    padding: 30px 0;
    border-bottom: 1px solid rgba(255,255,255,0.1);
}

.back-link {
    color: rgba(255,255,255,0.6);
    text-decoration: none;
    font-size: 14px;
    display: inline-flex;
    align-items: center;
    gap: 8px;
    transition: color 0.3s;
}

.back-link:hover {
    color: white;
}

/* Hero sekce */
.hero-section {
    padding: 80px 0;
    text-align: center;
}

.module-label {
    display: inline-block;
    padding: 8px 20px;
    border: 1px solid rgba(255,255,255,0.3);
    border-radius: 25px;
    font-size: 12px;
    font-weight: 600;
    letter-spacing: 2px;
    margin-bottom: 30px;
    text-transform: uppercase;
}

h1 {
    font-size: 72px;
    font-weight: 300;
    letter-spacing: -2px;
    margin-bottom: 30px;
    color: white;
}

.hero-section p {
    color: rgba(255,255,255,0.85);
}

.video-placeholder {
    width: 100%;
    aspect-ratio: 16/9;
    background: rgba(255,255,255,0.05);
    border-radius: 12px;
    display: flex;
    align-items: center;
    justify-content: center;
    margin: 40px 0;
    border: 1px solid rgba(255,255,255,0.1);
    cursor: pointer;
    transition: all 0.3s;
}

.video-placeholder:hover {
    background: rgba(255,255,255,0.08);
}

.video-placeholder svg {
    width: 60px;
    height: 60px;
    opacity: 0.5;
}

/* Úvodní text */
.intro-section {
    padding: 60px 0 100px 0;
}

.intro-section h2 {
    font-size: 36px;
    font-weight: 400;
    margin-bottom: 30px;
    color: white;
}

.intro-section h3 {
    font-size: 24px;
    font-weight: 500;
    margin: 40px 0 20px;
    color: white;
}

.intro-section p {
    font-size: 17px;
    line-height: 1.8;
    color: rgba(255,255,255,0.85);
    margin-bottom: 20px;
}

.highlight-box {
    background: rgba(255,255,255,0.05);
    border-left: 3px solid white;
    padding: 25px 30px;
    margin: 40px 0;
    border-radius: 8px;
}

.highlight-box p {
    color: rgba(255,255,255,0.9);
}

.learning-list {
    list-style: none;
    margin: 30px 0;
}

.learning-list li {
    padding: 12px 0;
    padding-left: 35px;
    position: relative;
    font-size: 16px;
    color: rgba(255,255,255,0.85);
}

.learning-list li:before {
    content: "✓";
    position: absolute;
    left: 0;
    color: #4CAF50;
    font-weight: bold;
    font-size: 20px;
}

/* SEKCE 2: CVIČENÍ (bílé pozadí) */
.exercises-wrapper {
    background: white;
    color: #333;
    padding: 80px 0;
}

.exercises-wrapper h2 {
    color: #000;
    font-size: 36px;
    font-weight: 400;
    margin-bottom: 30px;
}

.exercises-wrapper h3 {
    color: #000;
    font-size: 24px;
    font-weight: 500;
    margin: 40px 0 20px;
}

.exercises-wrapper h4 {
    color: #000;
}

.exercises-wrapper p {
    color: #333;
    font-size: 17px;
    line-height: 1.8;
    margin-bottom: 20px;
}

.exercises-wrapper ul li {
    color: #333;
}

/* Taby pro cvičení */
.exercise-tabs {
    display: flex;
    gap: 20px;
    margin-bottom: 60px;
    border-bottom: 1px solid rgba(0,0,0,0.1);
    justify-content: center;
}

.tab-btn {
    background: none;
    border: none;
    color: rgba(0,0,0,0.5);
    padding: 15px 30px;
    font-size: 16px;
    font-weight: 500;
    cursor: pointer;
    transition: all 0.3s;
    position: relative;
}

.tab-btn:hover {
    color: rgba(0,0,0,0.8);
}

.tab-btn.active {
    color: #000;
}

.tab-btn.active::after {
    content: '';
    position: absolute;
    bottom: -1px;
    left: 0;
    right: 0;
    height: 2px;
    background: #000;
}

/* Obsah cvičení */
.exercise-content {
    display: none;
}

.exercise-content.active {
    display: block;
    animation: fadeIn 0.3s ease-in;
}

@keyframes fadeIn {
    from {
        opacity: 0;
    }
    to {
        opacity: 1;
    }
}

/* Hlava cvičení */
.exercise-header {
    margin-bottom: 40px;
}

.exercise-header h2 {
    color: #000;
    font-size: 32px;
    margin-bottom: 15px;
}

.exercise-header p {
    color: #666;
    font-size: 16px;
}

/* Pracovní list */
.worksheet-section {
    margin: 40px 0;
    padding: 30px;
    background: #f9f9f9;
    border-radius: 8px;
    border: 1px solid #eee;
}

.worksheet-section h3 {
    font-size: 20px;
    margin-bottom: 20px;
}

.form-group {
    margin-bottom: 25px;
}

.form-group label {
    display: block;
    margin-bottom: 8px;
    font-weight: 500;
    color: #333;
    font-size: 15px;
}

.form-group textarea {
    width: 100%;
    min-height: 120px;
    padding: 15px;
    border: 1px solid #ddd;
    border-radius: 6px;
    font-family: 'Open Sans', sans-serif;
    font-size: 14px;
    resize: vertical;
    transition: border-color 0.3s;
}

.form-group textarea:focus {
    outline: none;
    border-color: #4CAF50;
    box-shadow: 0 0 0 2px rgba(76, 175, 80, 0.1);
}

/* Input fieldy (date, number, text) */
.form-group input[type="date"],
.form-group input[type="number"],
.form-group input[type="text"] {
    width: 100%;
    padding: 15px;
    border: 1px solid #ddd;
    border-radius: 6px;
    font-family: 'Open Sans', sans-serif;
    font-size: 14px;
    transition: border-color 0.3s, box-shadow 0.3s;
    height: 50px;
    background: white;
}

.form-group input[type="date"]:focus,
.form-group input[type="number"]:focus,
.form-group input[type="text"]:focus {
    outline: none;
    border-color: #4CAF50;
    box-shadow: 0 0 0 2px rgba(76, 175, 80, 0.1);
}

/* Kontejner pro řádek formuláře - více polí vedle sebe */
.form-row {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
    gap: 20px;
    margin-bottom: 25px;
}

.form-row .form-group {
    margin-bottom: 0;
}

/* Tlačítka */
.btn-group {
    display: flex;
    gap: 15px;
    margin-top: 30px;
    flex-wrap: wrap;
}

.btn {
    padding: 12px 24px;
    background: #f0f0f0;
    border: 1px solid #ddd;
    border-radius: 6px;
    cursor: pointer;
    font-size: 14px;
    font-weight: 500;
    transition: all 0.3s;
    font-family: 'Open Sans', sans-serif;
}

.btn:hover {
    background: #e0e0e0;
    border-color: #bbb;
}

.btn-primary {
    background: #4CAF50;
    color: white;
    border: none;
}

.btn-primary:hover {
    background: #45a049;
}

.success-message {
    color: #4CAF50;
    font-weight: 600;
}

/* SEKCE 3: ZÁVĚR + FOOTER (černé pozadí) */
.conclusion-wrapper {
    background: white;
}

/* Footer */
.footer {
    background: #000;
    color: white;
    padding: 40px 0;
    margin-top: 60px;
    border-top: 1px solid rgba(255,255,255,0.1);
}

.footer-content {
    text-align: center;
}

.footer-copyright {
    font-size: 14px;
    color: rgba(255,255,255,0.6);
    margin-bottom: 10px;
}

.footer-credits {
    font-size: 13px;
    color: rgba(255,255,255,0.5);
}

.footer-credits a {
    color: rgba(255,255,255,0.8);
    text-decoration: none;
    transition: color 0.3s;
}

.footer-credits a:hover {
    color: white;
}

/* Notifikace */
.notification {
    position: fixed;
    bottom: 20px;
    right: 20px;
    background: #4CAF50;
    color: white;
    padding: 15px 25px;
    border-radius: 6px;
    box-shadow: 0 4px 12px rgba(0,0,0,0.2);
    opacity: 0;
    transform: translateY(20px);
    transition: all 0.3s ease;
    z-index: 1000;
    pointer-events: none;
}

.notification.show {
    opacity: 1;
    transform: translateY(0);
    pointer-events: auto;
}

/* Responzivní design */
@media (max-width: 768px) {
    .container {
        padding: 0 20px;
    }

    h1 {
        font-size: 48px;
    }

    .intro-section h2,
    .exercises-wrapper h2 {
        font-size: 28px;
    }

    .intro-section h3,
    .exercises-wrapper h3 {
        font-size: 20px;
    }

    .exercise-tabs {
        flex-wrap: wrap;
        gap: 10px;
    }

    .tab-btn {
        padding: 12px 20px;
        font-size: 14px;
    }

    .btn-group {
        flex-direction: column;
    }

    .btn {
        width: 100%;
    }

    .worksheet-section {
        padding: 20px;
    }

    .form-group textarea {
        min-height: 100px;
    }
}

@media (max-width: 480px) {
    .container {
        padding: 0 15px;
    }

    h1 {
        font-size: 36px;
        letter-spacing: -1px;
    }

    .hero-section {
        padding: 40px 0;
    }

    .intro-section {
        padding: 40px 0 60px 0;
    }

    .exercises-wrapper {
        padding: 40px 0;
    }

    .intro-section h2,
    .exercises-wrapper h2 {
        font-size: 24px;
    }

    .intro-section h3,
    .exercises-wrapper h3 {
        font-size: 18px;
    }

    .module-label {
        font-size: 11px;
        padding: 6px 15px;
    }

    .video-placeholder svg {
        width: 40px;
        height: 40px;
    }

    .tab-btn {
        padding: 10px 15px;
        font-size: 13px;
    }

    .worksheet-section {
        padding: 15px;
    }

    .form-group textarea {
        min-height: 80px;
        font-size: 13px;
    }

    .btn {
        padding: 10px 16px;
        font-size: 13px;
    }
}