:root {
    /* Light Theme - Crystal Clear Water */
    --bg-gradient: linear-gradient(135deg, #e0f2f1 0%, #b2ebf2 50%, #80deea 100%);
    --glass-bg: rgba(255, 255, 255, 0.65);
    --glass-border: rgba(255, 255, 255, 0.8);
    --glass-shadow: 0 10px 40px rgba(0, 100, 120, 0.15);
    --text-main: #004d40;
    --text-muted: #00796b;
    --accent: #0097a7;
    --card-hover: rgba(255, 255, 255, 0.95);
    --wave-color: rgba(255, 255, 255, 0.4);
    
    /* Highly visible Badges */
    --badge-video: #ffebee;
    --badge-video-text: #c62828;
    --badge-playlist: #f3e5f5;
    --badge-playlist-text: #6a1b9a;
    --badge-book: #e8f5e9;
    --badge-book-text: #2e7d32;
    --badge-level: #e0f7fa;
    --badge-level-text: #006064;

    /* Checkbox contrast */
    --checkbox-bg: #ffffff;
    --checkbox-border: #00796b;
    --checkbox-check: #ffffff;
    
    --ripple-color: rgba(0, 151, 167, 0.15);
}

body.dark-theme {
    /* Dark Theme - Bioluminescent Deep Ocean */
    --bg-gradient: linear-gradient(135deg, #050b14 0%, #0a192f 50%, #112240 100%);
    --glass-bg: rgba(16, 31, 51, 0.65);
    --glass-border: rgba(100, 255, 218, 0.15);
    --glass-shadow: 0 15px 35px rgba(0, 0, 0, 0.6);
    --text-main: #e6f1ff;
    --text-muted: #8892b0;
    --accent: #64ffda;
    --card-hover: rgba(23, 42, 69, 0.85);
    --wave-color: rgba(100, 255, 218, 0.05);
    
    /* Bright Badges for dark mode */
    --badge-video: rgba(255, 82, 82, 0.2);
    --badge-video-text: #ff8a80;
    --badge-playlist: rgba(178, 101, 248, 0.2);
    --badge-playlist-text: #b388ff;
    --badge-book: rgba(76, 175, 80, 0.2);
    --badge-book-text: #69f0ae;
    --badge-level: rgba(100, 255, 218, 0.1);
    --badge-level-text: #64ffda;

    /* Checkbox contrast */
    --checkbox-bg: rgba(10, 25, 47, 0.9);
    --checkbox-border: #64ffda;
    --checkbox-check: #050b14;

    --ripple-color: rgba(100, 255, 218, 0.15);
}

* {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
    font-family: 'Outfit', sans-serif;
    transition: background-color 0.4s ease, color 0.4s ease, border-color 0.4s ease;
}

body {
    background: var(--bg-gradient);
    color: var(--text-main);
    min-height: 100vh;
    overflow-x: hidden;
    position: relative;
    padding-bottom: 100px; /* Space for waves */
}

/* Water Background Animations */
.water-background {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    z-index: -1;
    overflow: hidden;
    pointer-events: none;
}

.wave {
    position: absolute;
    bottom: 0;
    left: 0;
    width: 200%;
    height: 120px;
    background: url('data:image/svg+xml;utf8,<svg viewBox="0 0 1200 120" xmlns="http://www.w3.org/2000/svg"><path d="M0,0V46.29c47.79,22.2,103.59,32.17,158,28,70.36-5.37,136.33-33.31,206.8-37.5C438.64,32.43,512.34,53.67,583,72.05c69.27,18,138.3,24.88,209.4,13.08,36.15-6,69.85-17.84,104.45-29.34C989.49,25,1113-14.29,1200,52.47V0Z" fill="currentColor" opacity=".25"/></svg>');
    background-size: 50% 120px;
    color: var(--wave-color);
}

.wave1 { animation: wave-anim 15s linear infinite; bottom: -20px; z-index: 3; opacity: 0.8;}
.wave2 { animation: wave-anim 20s linear infinite reverse; bottom: 0px; z-index: 2; opacity: 0.6;}
.wave3 { animation: wave-anim 25s linear infinite; bottom: 15px; z-index: 1; opacity: 0.4;}

@keyframes wave-anim {
    0% { transform: translateX(0); }
    100% { transform: translateX(-50%); }
}

.bubble {
    position: absolute;
    bottom: -50px;
    background: radial-gradient(circle at 30% 30%, rgba(255,255,255,0.9), rgba(255,255,255,0.2));
    border-radius: 50%;
    box-shadow: inset 0 0 10px rgba(255,255,255,0.6);
    animation: rise calc(6s + 6s * var(--r)) infinite ease-in;
    opacity: 0;
}

.bubble-1 { left: 15%; width: 45px; height: 45px; --r: 0.2; animation-delay: 1s; }
.bubble-2 { left: 35%; width: 25px; height: 25px; --r: 0.6; animation-delay: 3s; }
.bubble-3 { left: 55%; width: 65px; height: 65px; --r: 0.1; animation-delay: 2s; }
.bubble-4 { left: 75%; width: 35px; height: 35px; --r: 0.8; animation-delay: 0s; }
.bubble-5 { left: 85%; width: 55px; height: 55px; --r: 0.4; animation-delay: 4s; }
.bubble-6 { left: 92%; width: 20px; height: 20px; --r: 0.9; animation-delay: 1.5s; }

@keyframes rise {
    0% { transform: translateY(0) scale(1); opacity: 0.7; }
    100% { transform: translateY(-110vh) scale(1.3); opacity: 0; }
}

/* Layout */
.app-container {
    max-width: 1300px;
    margin: 0 auto;
    padding: 2.5rem;
    position: relative;
    z-index: 10;
}

/* Glass Header */
.glass-header {
    background: var(--glass-bg);
    backdrop-filter: blur(20px);
    -webkit-backdrop-filter: blur(20px);
    border: 1px solid var(--glass-border);
    box-shadow: var(--glass-shadow);
    border-radius: 24px;
    padding: 1.5rem 2.5rem;
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 3.5rem;
    animation: slideDown 0.8s cubic-bezier(0.175, 0.885, 0.32, 1.275);
}

.logo {
    display: flex;
    align-items: center;
    gap: 18px;
}

.logo-icon {
    background: var(--accent);
    color: var(--checkbox-check);
    width: 48px;
    height: 48px;
    border-radius: 14px;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 1.5rem;
    box-shadow: 0 4px 15px rgba(0,0,0,0.1);
}

.logo-text h1 {
    font-size: 1.8rem;
    font-weight: 800;
    letter-spacing: 0.5px;
    line-height: 1.1;
}

.logo-text p {
    font-size: 0.85rem;
    font-weight: 500;
    color: var(--text-muted);
    letter-spacing: 1px;
    text-transform: uppercase;
}

.controls {
    display: flex;
    align-items: center;
    gap: 3rem;
}

.progress-tracker {
    display: flex;
    flex-direction: column;
    align-items: flex-end;
    gap: 8px;
}

.progress-text {
    font-weight: 600;
    font-size: 0.95rem;
    color: var(--text-muted);
}

.highlight-text {
    color: var(--accent);
    font-weight: 800;
    font-size: 1.1rem;
}

.progress-bar {
    width: 180px;
    height: 10px;
    background: rgba(128,128,128,0.2);
    border-radius: 20px;
    overflow: hidden;
    box-shadow: inset 0 1px 3px rgba(0,0,0,0.1);
}

.progress-fill {
    height: 100%;
    width: 0%;
    background: var(--accent);
    border-radius: 20px;
    transition: width 0.6s cubic-bezier(0.25, 0.46, 0.45, 0.94);
    box-shadow: 0 0 10px var(--accent);
}

/* Theme Toggle */
.theme-switch {
    position: relative;
    display: inline-block;
    width: 68px;
    height: 36px;
}

.theme-switch input {
    opacity: 0;
    width: 0;
    height: 0;
}

.slider {
    position: absolute;
    cursor: pointer;
    top: 0; left: 0; right: 0; bottom: 0;
    background-color: rgba(128,128,128,0.15);
    backdrop-filter: blur(5px);
    border: 2px solid var(--glass-border);
    transition: .4s;
    border-radius: 36px;
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 0 10px;
    box-shadow: inset 0 2px 5px rgba(0,0,0,0.1);
}

.slider .fa-sun { color: #f9a826; font-size: 15px; z-index: 1;}
.slider .fa-moon { color: #8892b0; font-size: 15px; z-index: 1;}

.slider:before {
    position: absolute;
    content: "";
    height: 28px;
    width: 28px;
    left: 2px;
    bottom: 2px;
    background-color: var(--text-main);
    transition: .4s cubic-bezier(0.68, -0.55, 0.265, 1.55);
    border-radius: 50%;
    z-index: 2;
    box-shadow: 0 2px 6px rgba(0,0,0,0.2);
}

input:checked + .slider {
    background-color: rgba(0,0,0,0.4);
}

input:checked + .slider:before {
    transform: translateX(32px);
    background-color: var(--accent);
}
input:checked + .slider .fa-moon { color: #fff; }

/* Course Grid */
.course-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(360px, 1fr));
    gap: 2.5rem;
}

/* Language Category Block */
.lang-category {
    margin-bottom: 1rem;
    animation: fadeIn 0.8s cubic-bezier(0.39, 0.575, 0.565, 1) both;
}

.lang-title {
    font-size: 1.6rem;
    font-weight: 800;
    margin-bottom: 1.2rem;
    padding-left: 0.8rem;
    border-left: 5px solid var(--accent);
    color: var(--text-main);
    display: flex;
    align-items: center;
    gap: 12px;
}

.lang-title i {
    color: var(--accent);
    opacity: 0.8;
}

.cards-wrapper {
    display: grid;
    grid-template-columns: 1fr;
    gap: 1.2rem;
}

/* Resource Card (Glassmorphism) */
.resource-card {
    background: var(--glass-bg);
    backdrop-filter: blur(16px);
    -webkit-backdrop-filter: blur(16px);
    border: 1px solid var(--glass-border);
    box-shadow: var(--glass-shadow);
    border-radius: 18px;
    padding: 1.4rem;
    display: flex;
    align-items: center;
    justify-content: space-between;
    transition: all 0.3s cubic-bezier(0.175, 0.885, 0.32, 1.275);
    text-decoration: none;
    color: var(--text-main);
    position: relative;
    overflow: hidden;
    cursor: pointer;
}

.resource-card:hover {
    transform: translateY(-6px) scale(1.02);
    background: var(--card-hover);
    box-shadow: 0 18px 45px rgba(0, 0, 0, 0.15);
    border-color: var(--accent);
}

/* Ripple Effect */
.ripple {
    position: absolute;
    border-radius: 50%;
    transform: scale(0);
    animation: ripple-animation 0.7s cubic-bezier(0.25, 0.46, 0.45, 0.94);
    background-color: var(--ripple-color);
    pointer-events: none;
}

@keyframes ripple-animation {
    to {
        transform: scale(3.5);
        opacity: 0;
    }
}

.card-content {
    display: flex;
    flex-direction: column;
    gap: 0.8rem;
    flex-grow: 1;
    z-index: 1;
}

.card-title {
    font-weight: 700;
    font-size: 1.15rem;
    display: flex;
    align-items: center;
    gap: 10px;
}

.badges {
    display: flex;
    gap: 10px;
    flex-wrap: wrap;
}

.badge {
    padding: 6px 12px;
    border-radius: 8px;
    font-size: 0.75rem;
    font-weight: 800;
    text-transform: uppercase;
    letter-spacing: 0.8px;
    display: flex;
    align-items: center;
    gap: 5px;
}

.badge i {
    font-size: 0.8rem;
}

.badge-video { background: var(--badge-video); color: var(--badge-video-text); }
.badge-playlist { background: var(--badge-playlist); color: var(--badge-playlist-text); }
.badge-book { background: var(--badge-book); color: var(--badge-book-text); }
.badge-level { background: var(--badge-level); color: var(--badge-level-text); }

/* Custom Checkbox */
.checkbox-wrapper {
    position: relative;
    width: 36px;
    height: 36px;
    z-index: 2;
    display: flex;
    align-items: center;
    justify-content: center;
    margin-left: 15px;
}

.checkbox-wrapper input {
    display: none;
}

.checkmark {
    width: 28px;
    height: 28px;
    background: var(--checkbox-bg);
    border: 3px solid var(--checkbox-border);
    border-radius: 8px;
    display: flex;
    align-items: center;
    justify-content: center;
    cursor: pointer;
    transition: all 0.4s cubic-bezier(0.68, -0.55, 0.265, 1.55);
    box-shadow: 0 4px 10px rgba(0,0,0,0.05);
}

.checkmark i {
    color: var(--checkbox-check);
    font-size: 14px;
    font-weight: 900;
    opacity: 0;
    transform: scale(0.2) rotate(-45deg);
    transition: all 0.4s cubic-bezier(0.68, -0.55, 0.265, 1.55);
}

.checkbox-wrapper input:checked + .checkmark {
    background: var(--accent);
    border-color: var(--accent);
    transform: rotate(360deg);
    box-shadow: 0 4px 15px rgba(0, 151, 167, 0.4);
}

.checkbox-wrapper input:checked + .checkmark i {
    opacity: 1;
    transform: scale(1) rotate(0deg);
}

/* Card Completed State */
.resource-card.completed {
    opacity: 0.6;
    background: rgba(128,128,128,0.05);
    border-color: transparent;
}

.resource-card.completed .card-title {
    text-decoration: line-through;
    color: var(--text-muted);
}

.resource-card.completed:hover {
    opacity: 0.8;
    transform: translateY(-3px);
}

/* Link Wrapper */
.card-link {
    text-decoration: none;
    color: inherit;
    display: flex;
    flex-grow: 1;
}

/* Animations */
@keyframes slideDown {
    from { transform: translateY(-30px); opacity: 0; }
    to { transform: translateY(0); opacity: 1; }
}

@keyframes fadeIn {
    from { opacity: 0; transform: translateY(30px) scale(0.95); }
    to { opacity: 1; transform: translateY(0) scale(1); }
}

/* Responsive */
@media (max-width: 900px) {
    .controls {
        gap: 1.5rem;
    }
    .progress-bar {
        width: 120px;
    }
}

@media (max-width: 768px) {
    .app-container {
        padding: 1.5rem;
    }
    .glass-header {
        flex-direction: column;
        gap: 2rem;
        text-align: center;
        padding: 1.5rem;
        border-radius: 20px;
    }
    .logo {
        flex-direction: column;
        gap: 10px;
    }
    .controls {
        flex-direction: column-reverse;
        width: 100%;
        gap: 1.5rem;
    }
    .progress-tracker {
        align-items: center;
        width: 100%;
    }
    .progress-bar {
        width: 100%;
        max-width: 300px;
    }
    .course-grid {
        grid-template-columns: 1fr;
    }
    .resource-card {
        padding: 1.2rem;
    }
    .card-title {
        font-size: 1.1rem;
    }
}