/* ============================================
   CSS Variables - Dark Mode Native Theme
   ============================================ */
:root {
    --color-bg-primary: #121212;
    --color-bg-secondary: #1e1e1e;
    --color-bg-tertiary: #2a2a2a;
    --color-text-primary: #ffffff;
    --color-text-secondary: #b0b0b0;
    --color-accent: #007bff;
    --color-accent-hover: #0056b3;
    --color-danger: #dc3545;
    --color-danger-hover: #c82333;
    --color-success: #28a745;

    --font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol";

    --spacing-xs: 0.5rem;
    --spacing-sm: 1rem;
    --spacing-md: 1.5rem;
    --spacing-lg: 2rem;
    --spacing-xl: 3rem;

    --border-radius: 8px;
    --transition-speed: 0.3s;

    --max-width: 1200px;
}

/* ============================================
   CSS Reset & Base Styles
   ============================================ */
* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

html {
    font-size: 16px;
    scroll-behavior: smooth;
}

body {
    font-family: var(--font-family);
    background-color: var(--color-bg-primary);
    color: var(--color-text-primary);
    line-height: 1.6;
    min-height: 100vh;
    display: flex;
    flex-direction: column;
    overflow-x: hidden;
}

/* ============================================
   Typography
   ============================================ */
h1, h2, h3, h4, h5, h6 {
    font-weight: 700;
    line-height: 1.2;
    margin-bottom: var(--spacing-sm);
}

h1 {
    font-size: 2.5rem;
}

h2 {
    font-size: 2rem;
    margin-bottom: var(--spacing-md);
}

h3 {
    font-size: 1.5rem;
}

p {
    margin-bottom: var(--spacing-sm);
}

a {
    color: var(--color-accent);
    text-decoration: none;
    transition: color var(--transition-speed);
}

a:hover {
    color: var(--color-accent-hover);
}

/* ============================================
   Layout Utilities
   ============================================ */
.container {
    max-width: var(--max-width);
    margin: 0 auto;
    padding: 0 var(--spacing-md);
    width: 100%;
}

main {
    flex: 1;
}

/* ============================================
   Header
   ============================================ */
.site-header {
    background-color: var(--color-bg-secondary);
    padding: var(--spacing-lg) 0;
    text-align: center;
    border-bottom: 1px solid var(--color-bg-tertiary);
}

.logo {
    font-size: 2.5rem;
    font-weight: 800;
    background: linear-gradient(135deg, var(--color-accent), #00d4ff);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
    margin-bottom: var(--spacing-xs);
}

.tagline {
    color: var(--color-text-secondary);
    font-size: 1rem;
    font-weight: 300;
    margin-bottom: 0;
}

/* ============================================
   Sections
   ============================================ */
.screen-tools-section,
.video-directory-section {
    padding: var(--spacing-xl) 0;
}

.section-description {
    text-align: center;
    color: var(--color-text-secondary);
    font-size: 1.125rem;
    margin-bottom: var(--spacing-lg);
}

.screen-tools-section h2,
.video-directory-section h2 {
    text-align: center;
}

/* ============================================
   Quick Tools Bar
   ============================================ */
.quick-tools-bar {
    background-color: var(--color-bg-secondary);
    border-bottom: 1px solid var(--color-bg-tertiary);
    padding: var(--spacing-md) 0;
    position: sticky;
    top: 0;
    z-index: 100;
}

.quick-tools-flex {
    display: flex;
    gap: var(--spacing-sm);
    justify-content: center;
    align-items: center;
}

.btn-tool {
    background-color: var(--color-bg-tertiary);
    color: var(--color-text-primary);
    padding: 0.75rem 1.5rem;
    border: 1px solid var(--color-accent);
    font-size: 0.9375rem;
    display: flex;
    align-items: center;
    gap: var(--spacing-xs);
}

.btn-tool:hover {
    background-color: var(--color-accent);
    transform: translateY(-1px);
    box-shadow: 0 4px 12px rgba(0, 123, 255, 0.3);
}

.tool-icon {
    font-size: 1.25rem;
}

/* ============================================
   Buttons
   ============================================ */
.btn {
    display: inline-block;
    padding: 0.75rem 1.5rem;
    font-size: 1rem;
    font-weight: 600;
    text-align: center;
    border: none;
    border-radius: var(--border-radius);
    cursor: pointer;
    transition: all var(--transition-speed);
    font-family: var(--font-family);
}

.btn-primary {
    background-color: var(--color-accent);
    color: var(--color-text-primary);
}

.btn-primary:hover {
    background-color: var(--color-accent-hover);
    transform: translateY(-2px);
    box-shadow: 0 4px 12px rgba(0, 123, 255, 0.3);
}

.btn-danger {
    background-color: var(--color-danger);
    color: var(--color-text-primary);
}

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

.btn-secondary {
    background-color: var(--color-bg-tertiary);
    color: var(--color-text-primary);
    border: 1px solid var(--color-text-secondary);
}

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

/* ============================================
   Filter Tabs
   ============================================ */
.filter-tabs {
    display: flex;
    flex-wrap: wrap;
    justify-content: center;
    gap: var(--spacing-sm);
    margin-bottom: var(--spacing-lg);
}

.filter-tab {
    padding: 0.625rem 1.25rem;
    background-color: var(--color-bg-secondary);
    color: var(--color-text-secondary);
    border: 1px solid var(--color-bg-tertiary);
    border-radius: 20px;
    cursor: pointer;
    transition: all var(--transition-speed);
    font-family: var(--font-family);
    font-size: 0.9375rem;
    font-weight: 500;
}

.filter-tab:hover {
    background-color: var(--color-bg-tertiary);
    color: var(--color-text-primary);
}

.filter-tab.active {
    background-color: var(--color-accent);
    color: var(--color-text-primary);
    border-color: var(--color-accent);
}

/* ============================================
   Video Grid
   ============================================ */
.video-directory-section {
    padding: var(--spacing-lg) 0 var(--spacing-xl);
}

.video-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(220px, 1fr));
    gap: var(--spacing-md);
}

.video-card {
    background-color: var(--color-bg-secondary);
    border: 2px solid var(--color-bg-tertiary);
    border-radius: var(--border-radius);
    overflow: hidden;
    cursor: pointer;
    transition: all var(--transition-speed);
    animation: fadeIn 0.4s ease-in;
    position: relative;
}

.video-card:hover {
    transform: scale(1.03);
    border-color: var(--color-accent);
    box-shadow: 0 8px 24px rgba(0, 123, 255, 0.4);
}

.video-card:hover .video-thumbnail img {
    transform: scale(1.08);
}

.video-card:active {
    transform: scale(0.98);
}

.video-thumbnail {
    position: relative;
    width: 100%;
    padding-bottom: 56.25%; /* 16:9 Aspect Ratio */
    overflow: hidden;
    background-color: var(--color-bg-tertiary);
}

.video-thumbnail img {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    object-fit: cover;
    transition: transform var(--transition-speed);
}

/* Thumbnail-only: No info section needed */
.video-info {
    display: none;
}

.video-title {
    display: none;
}

.video-category {
    display: none;
}

/* ============================================
   Fullscreen Overlay for Screen Tests
   ============================================ */
.fullscreen-overlay {
    position: fixed;
    top: 0;
    left: 0;
    width: 100vw;
    height: 100vh;
    z-index: 9999;
    display: flex;
    align-items: center;
    justify-content: center;
    background-color: #000000;
    cursor: pointer;
}

.fullscreen-overlay[hidden] {
    display: none;
}

.exit-hint {
    position: fixed;
    top: 20px;
    left: 50%;
    transform: translateX(-50%);
    background-color: rgba(0, 0, 0, 0.8);
    color: var(--color-text-primary);
    padding: var(--spacing-sm) var(--spacing-md);
    border-radius: var(--border-radius);
    font-size: 0.875rem;
    z-index: 10000;
    opacity: 0;
    animation: fadeInOut 3s ease-in-out;
}

@keyframes fadeInOut {
    0%, 100% {
        opacity: 0;
    }
    10%, 90% {
        opacity: 1;
    }
}

/* ============================================
   Modals
   ============================================ */
.modal {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background-color: rgba(0, 0, 0, 0.9);
    z-index: 10000;
    display: flex;
    align-items: center;
    justify-content: center;
    padding: var(--spacing-md);
    animation: fadeIn 0.3s ease-in;
}

.modal[hidden] {
    display: none;
}

.modal-content {
    background-color: var(--color-bg-secondary);
    border: 1px solid var(--color-bg-tertiary);
    border-radius: var(--border-radius);
    padding: var(--spacing-lg);
    max-width: 600px;
    width: 100%;
    position: relative;
    animation: slideUp 0.3s ease-out;
}

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

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

/* Warning Modal Specific Styles */
.warning-modal h2 {
    color: var(--color-danger);
    margin-bottom: var(--spacing-md);
    text-align: center;
}

.warning-modal p {
    margin-bottom: var(--spacing-sm);
    line-height: 1.6;
}

.warning-modal ul {
    margin: var(--spacing-sm) 0 var(--spacing-md) var(--spacing-lg);
    color: var(--color-text-secondary);
}

.warning-modal li {
    margin-bottom: var(--spacing-xs);
}

.warning-emphasis {
    font-weight: 600;
    color: var(--color-text-primary);
    margin-top: var(--spacing-md);
}

.modal-actions {
    display: flex;
    gap: var(--spacing-sm);
    margin-top: var(--spacing-lg);
    justify-content: center;
}

.modal-actions .btn {
    flex: 1;
    max-width: 200px;
}

/* Video Modal Specific Styles */
.video-modal-content {
    max-width: 900px;
}

.video-modal-content h3 {
    margin-bottom: var(--spacing-md);
    text-align: center;
}

.modal-close {
    position: absolute;
    top: var(--spacing-sm);
    right: var(--spacing-sm);
    background: none;
    border: none;
    color: var(--color-text-secondary);
    font-size: 2rem;
    cursor: pointer;
    line-height: 1;
    transition: color var(--transition-speed);
    padding: 0;
    width: 40px;
    height: 40px;
    display: flex;
    align-items: center;
    justify-content: center;
}

.modal-close:hover {
    color: var(--color-text-primary);
}

.video-wrapper {
    position: relative;
    width: 100%;
    padding-bottom: 56.25%; /* 16:9 Aspect Ratio */
    background-color: var(--color-bg-primary);
    border-radius: var(--border-radius);
    overflow: hidden;
}

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

/* ============================================
   SEO Content Section
   ============================================ */
.seo-content-section {
    background-color: var(--color-bg-secondary);
    border-top: 1px solid var(--color-bg-tertiary);
    padding: var(--spacing-xl) 0;
    margin-top: var(--spacing-xl);
}

.seo-content h2 {
    text-align: center;
    color: var(--color-text-primary);
    margin-bottom: var(--spacing-xl);
    font-size: 1.75rem;
}

.seo-columns {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: var(--spacing-lg);
    margin-bottom: var(--spacing-lg);
}

.seo-column h3 {
    color: var(--color-accent);
    font-size: 1.25rem;
    margin-bottom: var(--spacing-md);
}

.seo-column p {
    color: var(--color-text-secondary);
    line-height: 1.8;
    font-size: 0.9375rem;
}

.seo-keywords {
    background-color: var(--color-bg-tertiary);
    padding: var(--spacing-md);
    border-radius: var(--border-radius);
    border-left: 3px solid var(--color-accent);
    margin-top: var(--spacing-lg);
}

.seo-keywords p {
    color: var(--color-text-secondary);
    font-size: 0.875rem;
    line-height: 1.8;
    margin: 0;
}

.seo-keywords strong {
    color: var(--color-text-primary);
}

/* ============================================
   Footer
   ============================================ */
.site-footer {
    background-color: var(--color-bg-secondary);
    padding: var(--spacing-lg) 0;
    text-align: center;
    border-top: 1px solid var(--color-bg-tertiary);
}

.site-footer p {
    color: var(--color-text-secondary);
    font-size: 0.875rem;
    margin-bottom: var(--spacing-xs);
}

.footer-note {
    font-size: 0.75rem;
    opacity: 0.7;
}

/* ============================================
   Responsive Design - Media Queries
   ============================================ */

/* Tablets and below */
@media (max-width: 768px) {
    h1 {
        font-size: 2rem;
    }

    h2 {
        font-size: 1.75rem;
    }

    .logo {
        font-size: 2rem;
    }

    .quick-tools-flex {
        flex-direction: row;
        gap: var(--spacing-xs);
    }

    .btn-tool {
        font-size: 0.875rem;
        padding: 0.625rem 1rem;
    }

    .video-grid {
        grid-template-columns: repeat(auto-fill, minmax(180px, 1fr));
        gap: var(--spacing-sm);
    }

    .filter-tabs {
        gap: var(--spacing-xs);
    }

    .filter-tab {
        padding: 0.5rem 1rem;
        font-size: 0.875rem;
    }

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

    .modal-content {
        padding: var(--spacing-md);
    }

    .modal-actions {
        flex-direction: column;
    }

    .modal-actions .btn {
        max-width: 100%;
    }
}

/* Mobile devices */
@media (max-width: 480px) {
    html {
        font-size: 14px;
    }

    .site-header {
        padding: var(--spacing-md) 0;
    }

    .quick-tools-flex {
        flex-direction: column;
        width: 100%;
    }

    .btn-tool {
        width: 100%;
        justify-content: center;
    }

    .video-directory-section {
        padding: var(--spacing-md) 0 var(--spacing-lg);
    }

    .video-grid {
        grid-template-columns: repeat(2, 1fr);
        gap: var(--spacing-xs);
    }

    .filter-tab {
        font-size: 0.8125rem;
        padding: 0.5rem 0.75rem;
    }

    .exit-hint {
        font-size: 0.75rem;
        padding: var(--spacing-xs) var(--spacing-sm);
    }
}

/* Large screens */
@media (min-width: 1400px) {
    .video-grid {
        grid-template-columns: repeat(auto-fill, minmax(240px, 1fr));
    }
}

/* Extra large screens */
@media (min-width: 1800px) {
    .container {
        max-width: 1600px;
    }

    .video-grid {
        grid-template-columns: repeat(auto-fill, minmax(260px, 1fr));
    }
}

/* ============================================
   Accessibility & Focus States
   ============================================ */
button:focus,
a:focus,
.filter-tab:focus {
    outline: 2px solid var(--color-accent);
    outline-offset: 2px;
}

/* Reduce motion for users who prefer it */
@media (prefers-reduced-motion: reduce) {
    * {
        animation-duration: 0.01ms !important;
        animation-iteration-count: 1 !important;
        transition-duration: 0.01ms !important;
        scroll-behavior: auto !important;
    }
}

/* ============================================
   Loading States
   ============================================ */
.video-grid:empty::after {
    content: "Loading videos...";
    display: block;
    text-align: center;
    color: var(--color-text-secondary);
    padding: var(--spacing-xl);
    font-size: 1.125rem;
}

/* ============================================
   Print Styles
   ============================================ */
@media print {
    .site-header,
    .site-footer,
    .screen-tools-section,
    .filter-tabs,
    .modal {
        display: none;
    }

    body {
        background-color: white;
        color: black;
    }
}