:root {
    --bg-color: #f5f7fa;
    --text-color: #333;
    --card-bg: #ffffff;
    --primary-color: #ff0000; /* YouTube Red */
    --secondary-color: #282828;
    --accent-color: #3ea6ff;
    --border-color: #e0e0e0;
    --shadow-sm: 0 2px 5px rgba(0,0,0,0.05);
    --shadow-md: 0 4px 10px rgba(0,0,0,0.1);
    --radius-md: 12px;
    --radius-lg: 20px;
    --font-stack: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Oxygen, Ubuntu, Cantarell, "Open Sans", "Helvetica Neue", sans-serif;
}

body.dark-mode {
    --bg-color: #121212;
    --text-color: #e0e0e0;
    --card-bg: #1e1e1e;
    --primary-color: #ff4d4d;
    --secondary-color: #aaaaaa;
    --border-color: #333;
    --shadow-sm: 0 2px 5px rgba(0,0,0,0.3);
    --shadow-md: 0 4px 10px rgba(0,0,0,0.5);
}

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

body {
    font-family: var(--font-stack);
    background-color: var(--bg-color);
    color: var(--text-color);
    line-height: 1.6;
    transition: background-color 0.3s ease, color 0.3s ease;
}

/* Header */
.main-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 20px 40px;
    background-color: var(--card-bg);
    box-shadow: var(--shadow-sm);
    position: sticky;
    top: 0;
    z-index: 100;
}

.logo {
    font-size: 1.5rem;
    font-weight: 800;
    color: var(--primary-color);
    letter-spacing: -0.5px;
}

#theme-toggle {
    background: none;
    border: none;
    font-size: 1.5rem;
    cursor: pointer;
    padding: 8px;
    border-radius: 50%;
    transition: background-color 0.2s;
}

#theme-toggle:hover {
    background-color: var(--border-color);
}

/* Main Container */
.container {
    max-width: 900px;
    margin: 40px auto;
    padding: 0 20px;
}

/* Hero Section */
.hero-section {
    text-align: center;
    margin-bottom: 40px;
}

.hero-section h1 {
    font-size: 2.5rem;
    margin-bottom: 10px;
    font-weight: 700;
}

.subtitle {
    color: var(--secondary-color);
    font-size: 1.1rem;
    margin-bottom: 30px;
}

/* Input Group */
.input-group {
    display: flex;
    gap: 10px;
    max-width: 600px;
    margin: 0 auto;
    background: var(--card-bg);
    padding: 8px;
    border-radius: 50px; /* Pill shape */
    box-shadow: var(--shadow-md);
    border: 1px solid var(--border-color);
}

.input-group input {
    flex: 1;
    border: none;
    padding: 15px 20px;
    font-size: 1rem;
    outline: none;
    background: transparent;
    color: var(--text-color);
    border-radius: 50px;
}

.input-group button {
    background-color: var(--primary-color);
    color: white;
    border: none;
    padding: 15px 30px;
    border-radius: 40px;
    font-weight: 600;
    cursor: pointer;
    transition: transform 0.2s, background-color 0.2s;
}

.input-group button:hover {
    background-color: #d00000;
    transform: translateY(-1px);
}

.error-msg {
    color: #ff4d4d;
    font-weight: 500;
    margin-top: 15px;
    height: 24px; /* Prevent layout jump */
}

/* Ads */
.ad-container {
    margin: 30px 0;
    text-align: center;
}
.ad-placeholder {
    background: var(--card-bg);
    border: 2px dashed var(--border-color);
    padding: 20px;
    color: var(--secondary-color);
    border-radius: var(--radius-md);
    font-size: 0.9rem;
}

/* Results */
.result-section {
    display: flex;
    flex-direction: column;
    gap: 30px;
    margin-bottom: 60px;
}

.hidden {
    display: none !important;
}

.thumbnail-card {
    background: var(--card-bg);
    padding: 20px;
    border-radius: var(--radius-lg);
    box-shadow: var(--shadow-md);
    text-align: center;
    border: 1px solid var(--border-color);
}

.highlight-card {
    border: 2px solid var(--primary-color); /* Highlight the main result */
}

.thumbnail-card h3 {
    margin-bottom: 15px;
    font-size: 1.2rem;
    color: var(--text-color);
}

.img-wrapper {
    width: 100%;
    margin-bottom: 20px;
    overflow: hidden;
    border-radius: var(--radius-md);
    background-color: #000; /* Letterboxing background */
    min-height: 200px;
    display: flex;
    align-items: center;
    justify-content: center;
}

.img-wrapper img {
    max-width: 100%;
    height: auto;
    display: block;
}

.action-buttons {
    display: flex;
    justify-content: center;
    gap: 10px;
}

.download-btn {
    text-decoration: none;
    padding: 12px 24px;
    border-radius: 8px;
    font-weight: 600;
    transition: all 0.2s;
    display: inline-block;
}

.download-btn.primary {
    background-color: var(--primary-color);
    color: white;
}

.download-btn.secondary {
    background-color: transparent;
    border: 1px solid var(--border-color);
    color: var(--text-color);
}

.download-btn:hover {
    opacity: 0.9;
    transform: translateY(-2px);
}

/* Grid Layout for secondary images */
.grid-row {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 20px;
}

@media (max-width: 600px) {
    .grid-row {
        grid-template-columns: 1fr;
    }
    .input-group {
        flex-direction: column;
        border-radius: var(--radius-md);
        padding: 15px;
        gap: 15px;
    }
    .input-group input, .input-group button {
        width: 100%;
        border-radius: 8px;
    }
    .main-header {
        padding: 15px 20px;
    }
    .hero-section h1 {
        font-size: 1.8rem;
    }
}

/* SEO Content */
.seo-content {
    margin-top: 60px;
    padding-top: 40px;
    border-top: 1px solid var(--border-color);
}

.seo-content article {
    margin-bottom: 40px;
}

.seo-content h2 {
    font-size: 1.5rem;
    margin-bottom: 15px;
    color: var(--text-color);
}

.seo-content p, .seo-content li {
    color: var(--secondary-color);
    font-size: 1rem;
    margin-bottom: 10px;
}

.seo-content ol {
    padding-left: 20px;
}

.main-footer {
    text-align: center;
    padding: 40px;
    color: var(--secondary-color);
    font-size: 0.9rem;
    border-top: 1px solid var(--border-color);
    margin-top: 40px;
}