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

:root {
    --primary-color: #0066cc;
    --secondary-color: #004499;
    --accent-color: #00aaff;
    --success-color: #00cc66;
    --text-color: #333;
    --light-gray: #f5f5f5;
    --border-color: #ddd;
    --disabled-color: #999;
}

body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    color: var(--text-color);
    line-height: 1.6;
    background-color: #fff;
}

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

/* Header */
.header {
    background: linear-gradient(135deg, #0066cc, #004499);
    color: white;
    padding: 2rem 0;
    box-shadow: 0 4px 20px rgba(0, 0, 0, 0.3);
}

.header .container {
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.logo h1 {
    font-size: 2rem;
    font-weight: 700;
    letter-spacing: 2px;
}

.logo svg {
    height: 50px;
    width: auto;
    filter: brightness(0) invert(1);
}

.tagline {
    font-size: 0.9rem;
    color: #666;
    font-style: italic;
}

.nav {
    display: flex;
    gap: 2rem;
}

.nav-link {
    color: white;
    text-decoration: none;
    font-weight: 500;
    transition: color 0.3s, opacity 0.3s;
    opacity: 0.9;
}

.nav-link:hover {
    opacity: 1;
    color: white;
}

/* Main Content */
.main-content {
    padding: 3rem 0;
    min-height: calc(100vh - 200px);
}

.intro {
    text-align: center;
    margin-bottom: 2rem;
}

.intro h2 {
    color: var(--primary-color);
    font-size: 2rem;
    margin-bottom: 0.5rem;
}

.intro p {
    color: var(--text-color);
    font-size: 1.1rem;
}

/* Progress Bar */
.progress-bar {
    background-color: var(--light-gray);
    border-radius: 50px;
    height: 40px;
    margin: 2rem 0;
    overflow: hidden;
    border: 2px solid var(--border-color);
    position: relative;
}

.progress-fill {
    background: linear-gradient(90deg, var(--accent-color), var(--primary-color));
    height: 100%;
    width: 0%;
    transition: width 0.5s ease;
    display: flex;
    align-items: center;
    justify-content: center;
    border-radius: 50px;
}

.progress-text {
    color: white;
    font-weight: bold;
    font-size: 0.9rem;
    position: absolute;
    left: 50%;
    transform: translateX(-50%);
}

/* Video Items */
.video-item {
    background: white;
    border: 2px solid var(--border-color);
    border-radius: 12px;
    padding: 1.5rem;
    margin-bottom: 2rem;
    box-shadow: 0 4px 6px rgba(0, 0, 0, 0.1);
    transition: transform 0.3s, box-shadow 0.3s;
}

.video-item:hover {
    transform: translateY(-2px);
    box-shadow: 0 6px 12px rgba(0, 0, 0, 0.15);
}

.video-item.completed {
    border-color: var(--success-color);
    background-color: #f0fff8;
}

.video-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 1rem;
}

.video-title {
    color: var(--primary-color);
    font-size: 1.3rem;
    font-weight: 600;
}

.video-status {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    font-size: 0.9rem;
    color: var(--disabled-color);
}

.video-status.watching {
    color: var(--accent-color);
}

.video-status.completed {
    color: var(--success-color);
}

.status-icon {
    font-size: 1.2rem;
}

.video-description {
    color: #666;
    margin-bottom: 1rem;
    font-size: 0.95rem;
}

.video-container {
    position: relative;
    width: 100%;
    padding-bottom: 56.25%; /* 16:9 aspect ratio */
    margin-bottom: 1rem;
    background-color: #000;
    border-radius: 8px;
    overflow: hidden;
}

.video-container iframe {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
}

.video-progress-container {
    margin-bottom: 1rem;
}

.video-progress-bar {
    background-color: var(--light-gray);
    border-radius: 8px;
    height: 18px;
    overflow: hidden;
    border: 1px solid var(--border-color);
    position: relative;
}

.video-progress-fill {
    background: linear-gradient(90deg, var(--accent-color), var(--primary-color));
    height: 100%;
    width: 0%;
    transition: width 0.3s ease;
    border-radius: 8px;
}

.video-progress-text {
    color: #666;
    font-weight: 600;
    font-size: 0.7rem;
    position: absolute;
    left: 50%;
    top: 50%;
    transform: translate(-50%, -50%);
}

.video-footer {
    display: flex;
    justify-content: flex-start;
    align-items: center;
}

.checkbox-container {
    display: flex;
    align-items: center;
    gap: 0.5rem;
}

.checkbox-container input[type="checkbox"] {
    width: 20px;
    height: 20px;
    cursor: pointer;
}

.checkbox-container input[type="checkbox"]:disabled {
    cursor: not-allowed;
    opacity: 0.5;
}

.checkbox-container label {
    font-weight: 500;
    cursor: pointer;
}

.checkbox-container label.disabled {
    color: var(--disabled-color);
    cursor: not-allowed;
}

.watch-time {
    font-size: 0.9rem;
    color: #666;
}

/* Submit Section */
.submit-section {
    text-align: center;
    margin-top: 3rem;
    padding: 2rem;
    background-color: var(--light-gray);
    border-radius: 12px;
}

.submit-btn {
    background: linear-gradient(135deg, var(--success-color), #009955);
    color: white;
    border: none;
    padding: 1rem 3rem;
    font-size: 1.1rem;
    font-weight: 600;
    border-radius: 50px;
    cursor: pointer;
    transition: transform 0.3s, box-shadow 0.3s;
    box-shadow: 0 4px 15px rgba(0, 204, 102, 0.3);
}

.submit-btn:hover:not(:disabled) {
    transform: translateY(-2px);
    box-shadow: 0 6px 20px rgba(0, 204, 102, 0.4);
}

.submit-btn:disabled {
    background: linear-gradient(135deg, var(--disabled-color), #777);
    cursor: not-allowed;
    box-shadow: none;
}

.submit-info {
    margin-top: 1rem;
    color: var(--disabled-color);
    font-size: 0.95rem;
}

.submit-info.ready {
    color: var(--success-color);
    font-weight: 600;
}

/* Footer */
.footer {
    background-color: var(--secondary-color);
    color: white;
    padding: 1.5rem 0;
    text-align: center;
    margin-top: 3rem;
}

/* Success Modal */
.modal {
    display: none;
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background-color: rgba(0, 0, 0, 0.7);
    z-index: 1000;
    justify-content: center;
    align-items: center;
}

.modal.show {
    display: flex;
}

.modal-content {
    background: white;
    padding: 3rem;
    border-radius: 12px;
    text-align: center;
    max-width: 500px;
    box-shadow: 0 10px 40px rgba(0, 0, 0, 0.3);
}

.modal-content h2 {
    color: var(--success-color);
    font-size: 2rem;
    margin-bottom: 1rem;
}

.modal-content p {
    color: var(--text-color);
    font-size: 1.1rem;
    margin-bottom: 2rem;
}

.modal-btn {
    background: var(--primary-color);
    color: white;
    border: none;
    padding: 0.75rem 2rem;
    font-size: 1rem;
    font-weight: 600;
    border-radius: 50px;
    cursor: pointer;
    transition: background 0.3s;
}

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

/* Responsive */
@media (max-width: 768px) {
    .header .container {
        flex-direction: column;
        gap: 1rem;
    }

    .nav {
        gap: 1rem;
    }

    .video-header {
        flex-direction: column;
        align-items: flex-start;
        gap: 0.5rem;
    }

    .video-footer {
        flex-direction: column;
        gap: 1rem;
        align-items: flex-start;
    }

    .intro h2 {
        font-size: 1.5rem;
    }

    .logo h1 {
        font-size: 1.5rem;
    }

    .logo svg {
        height: 35px;
        filter: brightness(0) invert(1);
    }
}