:root {
    --color-bg-page: #f9f9f9;
    --color-bg-card: #ffffff;
    --color-text-primary: #1f2937;
    --color-text-secondary: #6b7280;
    --color-accent: #2563eb; 
    --color-accent-text: #ffffff;
    --color-border: #e5e7eb;
    --color-shadow: 0 4px 6px -1px rgba(0, 0, 0, 0.1), 0 2px 4px -2px rgba(0, 0, 0, 0.1);
}

/* Dark Mode */
body[data-theme='dark'] {
    --color-bg-page: #111827;
    --color-bg-card: #1f2937;
    --color-text-primary: #f3f4f6;
    --color-text-secondary: #9ca3af;
    --color-accent: #4f46e5;
    --color-accent-text: #ffffff;
    --color-border: #374151;
    --color-shadow: 0 10px 15px -3px rgba(0, 0, 0, 0.3), 0 4px 6px -4px rgba(0, 0, 0, 0.3);
}

/* Vibrant UI */
body[data-theme='vibrant'] {
    --color-bg-page: #f0fdf4;
    --color-bg-card: #ffffff;
    --color-text-primary: #16a34a; 
    --color-text-secondary: #65a30d;
    --color-accent: #10b981; 
    --color-accent-text: #ffffff;
    --color-border: #d1fae5;
    --color-shadow: 0 4px 6px -1px rgba(16, 185, 129, 0.2), 0 2px 4px -2px rgba(16, 185, 129, 0.1);
}

/* Minimalist Theme */
body[data-theme='minimalist'] {
    --color-bg-page: #ffffff;
    --color-bg-card: #ffffff;
    --color-text-primary: #000000;
    --color-text-secondary: #374151;
    --color-accent: #000000;
    --color-accent-text: #ffffff;
    --color-border: #d1d5db;
    --color-shadow: none;
}

/* Unacademy-Inspired Theme */
body[data-theme='unacademy-inspired'] {
    --color-bg-page: #ffffff;
    --color-bg-card: #ffffff;
    --color-text-primary: #212121;
    --color-text-secondary: #9aa1a7;
    --color-accent: #374151; 
    --color-accent-text: #ffffff;
    --color-border: #e9e9e9;
    --color-shadow: 0 1px 3px 0 rgba(0, 0, 0, 0.05), 0 1px 2px 0 rgba(0, 0, 0, 0.03);
}

body {
    font-family: 'Inter', sans-serif;
    transition: background-color 0.3s, color 0.3s;
    background-color: var(--color-bg-page);
    min-height: 100vh;
    position: relative;
}

/* Background Watermark */
#bg-watermark {
    position: fixed;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    width: 60%;
    max-width: 500px;
    opacity: 0.05; /* Very subtle */
    pointer-events: none;
    z-index: 0;
    filter: grayscale(100%);
}

.card {
    background-color: var(--color-bg-card);
    color: var(--color-text-primary);
    box-shadow: var(--color-shadow);
    border: 1px solid var(--color-border);
    transition: all 0.3s ease-in-out;
    position: relative;
    z-index: 10;
}

.card:hover {
    transform: translateY(-4px); 
    box-shadow: 0 10px 15px -3px rgba(0, 0, 0, 0.1), 0 4px 6px -2px rgba(0, 0, 0, 0.05);
}

.text-primary { color: var(--color-text-primary); }
.text-secondary { color: var(--color-text-secondary); }
.bg-accent { background-color: var(--color-accent); }
.text-accent { color: var(--color-accent); }
.text-accent-text { color: var(--color-accent-text); }
.border-accent { border-color: var(--color-accent); }
.border-border { border-color: var(--color-border); }

/* Custom Tab Styles */
.tab {
    color: var(--color-text-secondary);
    transition: color 0.2s;
    cursor: pointer;
}
.tab:hover {
    color: var(--color-text-primary);
}
.tab-active {
    color: var(--color-text-primary);
    font-weight: 600;
    border-bottom: 2px solid var(--color-accent);
}

/* Filter Buttons */
.filter-btn {
    padding: 6px 16px;
    border-radius: 9999px;
    font-size: 0.875rem;
    font-weight: 500;
    transition: all 0.2s;
    border: 1px solid var(--color-border);
    background-color: var(--color-bg-card);
    color: var(--color-text-secondary);
}
.filter-btn:hover {
    border-color: var(--color-accent);
    color: var(--color-accent);
}
.filter-btn.active {
    background-color: var(--color-accent);
    color: var(--color-accent-text);
    border-color: var(--color-accent);
}

/* Theme Button Styles */
.theme-btn {
    display: flex;
    align-items: center;
    padding: 8px 16px;
    border-radius: 6px;
    font-size: 14px;
    font-weight: 500;
    transition: all 0.2s ease;
    cursor: pointer;
    border: 1px solid var(--color-border);
    background-color: var(--color-bg-card);
    color: var(--color-text-primary);
}
.theme-btn:hover {
    background-color: var(--color-bg-page);
}
.theme-btn.active {
    background-color: var(--color-accent);
    color: var(--color-accent-text);
    border-color: var(--color-accent);
    box-shadow: 0 2px 4px rgba(0, 0, 0, 0.1);
}

/* Skeleton Loader Animation */
@keyframes shimmer {
    0% { background-position: -1000px 0; }
    100% { background-position: 1000px 0; }
}
.skeleton {
    animation: shimmer 2s infinite linear;
    background: linear-gradient(to right, var(--color-bg-card) 4%, var(--color-bg-page) 25%, var(--color-bg-card) 36%);
    background-size: 1000px 100%;
}

.content-feature-block:hover .arrow-icon { transform: translateX(4px); }
.content-feature-block .arrow-icon { transition: transform 0.2s ease-out; }
.content-feature-block { text-decoration: none; display: block; transition: all 0.3s ease-in-out; }