:root {
    /* Day Theme  */
    --primary-day: #1e3a8a;
    --secondary-day: #3b82f6;
    --accent-day: #8b5cf6;
    --bg-day: #f0f9ff;
    --card-bg-day: #ffffff;
    --text-day: #1e293b;
    --border-day: #cbd5e1;
    
    /* NIght Theme */
    --primary-night: #0f172a;
    --secondary-night: #1e293b;
    --accent-night: #7c3aed;
    --bg-night: #020617;
    --card-bg-night: #0f172a;
    --text-night: #e2e8f0;
    --border-night: #334155;
        
    /* Variable */
    --primary-color: var(--primary-day);
    --secondary-color: var(--secondary-day);
    --accent-color: var(--accent-day);
    --bg-color: var(--bg-day);
    --text-color: var(--text-day);
    --card-bg: var(--card-bg-day);
    --border-color: var(--border-day);
}

[data-theme="night"] {
    --primary-color: var(--primary-night);
    --secondary-color: var(--secondary-night);
    --accent-color: var(--accent-night);
    --bg-color: var(--bg-night);
    --text-color: var(--text-night);
    --card-bg: var(--card-bg-night);
    --border-color: var(--border-night);
}

body {
    background-color: var(--bg-color);
    color: var(--text-color);
    transition: all 0.5s ease;
    font-family: 'Segoe UI', Tahoma, Verdana, sans-serif;
    line-height: 1.6;
}

.navbar {
    background: linear-gradient(135deg, var(--primary-color) 0%, var(--accent-color) 100%) !important;
    box-shadow: 0 4px 15px rgba(0, 0, 0, 0.1);
    border-bottom: none;
}

.navbar-brand {
    font-weight: 700;
    font-size: 1.5rem;
}

/* button */
.btn-primary {
    background: linear-gradient(135deg, var(--primary-color), var(--accent-color));
    border: none;
    border-radius: 8px;
    font-weight: 600;
    transition: all 0.3s ease;
}

.btn-primary:hover {
    transform: translateY(-2px);
    box-shadow: 0 6px 20px rgba(30, 58, 138, 0.3);
}

.btn-outline-primary {
    border: 2px solid var(--primary-color);
    color: var(--primary-color);
    border-radius: 8px;
    font-weight: 600;
    transition: all 0.3s ease;
}

.btn-outline-primary:hover {
    background: linear-gradient(135deg, var(--primary-color), var(--accent-color));
    border-color: transparent;
    transform: translateY(-2px);
}

.card {
    background-color: var(--card-bg);
    border: 1px solid var(--border-color);
    border-radius: 12px;
    box-shadow: 0 4px 15px rgba(40, 78, 183, 0.176);
    transition: all 0.3s ease;
}

.card:hover {
    transform: translateY(-5px);
    box-shadow: 0 8px 25px rgba(37, 75, 179, 0.203);
}

.card-header {
    background: linear-gradient(135deg, var(--primary-color), var(--accent-color));
    color: white;
    border-bottom: none;
    border-radius: 12px 12px 0 0 !important;
    padding: 1rem 1.25rem;
}

/* .flashcard */
.flashcard-container {
    height: 250px;
    margin: 0 auto;
    max-width: 500px;
}

.flashcard {
    width: 100%;
    height: 100%;
    position: relative;
    transform-style: preserve-3d;
    transition: transform 0.6s cubic-bezier(0.4, 0, 0.2, 1);
    cursor: pointer;
    border-radius: 16px;
    box-shadow: 0 8px 32px rgba(0, 0, 0, 0.1);
}

.flashcard.flipped {
    transform: rotateY(180deg);
}

.flashcard-front,
.flashcard-back {
    position: absolute;
    width: 100%;
    height: 100%;
    backface-visibility: hidden;
    display: flex;
    align-items: center;
    justify-content: center;
    border: none;
    border-radius: 16px;
    padding: 2rem;
    background: linear-gradient(135deg, var(--primary-color), var(--accent-color));
    color: white;
}

.flashcard-back {
    background: linear-gradient(135deg, var(--secondary-color), var(--accent-color));
    transform: rotateY(180deg);
}

.flashcard-content {
    text-align: center;
    font-size: 1.2rem;
    font-weight: 500;
}

/* Learn Tabs */
.nav-tabs {
    border-bottom: 2px solid var(--border-color);
}

.nav-tabs .nav-link {
    border: none;
    color: var(--text-color);
    font-weight: 500;
    padding: 0.75rem 1.5rem;
    margin: 0 0.25rem;
    transition: all 0.3s ease;
}

.nav-tabs .nav-link:hover {
    border: none;
    background-color: rgba(30, 58, 138, 0.1);
}

.nav-tabs .nav-link.active {
    background: linear-gradient(135deg, var(--primary-color), var(--accent-color));
    color: white;
    border: none;
}

/* Progress Bar */
.progress {
    background-color: var(--border-color);
    border-radius: 10px;
    height: 8px;
    overflow: hidden;
}

.progress-bar {
    background: linear-gradient(90deg, var(--primary-color), var(--accent-color));
    border-radius: 10px;
    transition: width 0.6s ease;
}

/* .badges */
.badge {
    border-radius: 6px;
    font-weight: 500;
    padding: 0.5rem 0.75rem;
}

.bg-primary {
    background: linear-gradient(135deg, var(--primary-color), var(--accent-color)) !important;
}

.bg-secondary {
    background: linear-gradient(135deg, #64748b, #475569) !important;
}

/* Lists */
.list-group-item {
    background-color: var(--card-bg);
    border-color: var(--border-color);
    color: var(--text-color);
    padding: 1rem 1.25rem;
    transition: all 0.3s ease;
}

.list-group-item:hover {
    background-color: rgba(30, 58, 138, 0.05);
    transform: translateX(5px);
}

.list-group-item:first-child {
    border-top-left-radius: 8px;
    border-top-right-radius: 8px;
}

.list-group-item:last-child {
    border-bottom-left-radius: 8px;
    border-bottom-right-radius: 8px;
}

/* Forms */
.form-label, #description {
    background-color: var(--card-bg);
    color: var(--text-color);
    padding: 0.5rem;
}

.form-control, .form-select {
    background-color: var(--card-bg);
    border: 2px solid var(--border-color);
    color: var(--text-color);
    border-radius: 8px;
    padding: 0.75rem 1rem;
    transition: all 0.3s ease;
}

.form-control:focus, .form-select:focus {
    background-color: var(--card-bg);
    border-color: var(--accent-color);
    color: var(--text-color);
    box-shadow: 0 0 0 0.25rem rgba(139, 92, 246, 0.25);
}

/* placeholder  */
.form-control::placeholder {
    color: var(--text-day);
    opacity: 0.7;
}

[data-theme="night"] .form-control::placeholder {
    color: var(--text-night);
    opacity: 0.8;
}

/* Learn style */
.learn-content {
    background: var(--card-bg);
    border-radius: 12px;
    padding: 2rem;
    margin-bottom: 2rem;
}

.quiz-choice {
    transition: all 0.3s ease;
    border-radius: 8px;
}

.quiz-choice:hover {
    transform: translateX(10px);
    background-color: rgba(30, 58, 138, 0.05);
}

/* Gradient */
.gradient-bg {
    background: linear-gradient(135deg, var(--primary-color) 0%, var(--accent-color) 100%);
}

.gradient-text {
    background: linear-gradient(135deg, var(--primary-color), var(--accent-color));
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.card-title,
#quizScore,
.card-text {
    color: var(--text-day);
    transition: color 0.5s ease;
}

[data-theme="night"] .card-title,
[data-theme="night"] .card-text,
[data-theme="night"] #quizScore {
    color: var(--text-night);
}

/* َAnimation */
@keyframes fadeIn {
    from { opacity: 0; transform: translateY(20px); }
    to { opacity: 1; transform: translateY(0); }
}

.card, .btn, .form-control {
    animation: fadeIn 0.6s ease-out;
}

/* Empty state*/
.text-muted {
    color: #64748b !important;
}

/* Responsiveness */
@media (max-width: 768px) {
    .flashcard-container {
        height: 200px;
    }
    
    .flashcard-content {
        font-size: 1rem;
    }
    
    .btn-group {
        flex-wrap: wrap;
    }
    
    .btn-group .btn {
        margin-bottom: 0.25rem;
    }
    
    .progress {
        width: 120px !important;
        height: 6px; 
    }
    
    .text-end small {
        font-size: 0.75rem;
    }
    
    .text-end .text-muted {
        font-size: 0.7rem;
    }
}

/* Theme icon */
#themeToggle {
    border: 2px solid rgba(255, 255, 255, 0.3);
    border-radius: 50%;
    width: 40px;
    height: 40px;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: all 0.3s ease;
    background: rgba(255, 255, 255, 0.1);
    backdrop-filter: blur(10px);
}

#themeToggle:hover {
    transform: rotate(30deg);
    background: rgba(255, 255, 255, 0.2);
}

[data-theme="night"] body {
    background: linear-gradient(135deg,  var(--bg-night) 0%, #1e1b4b 100%);
    position: relative;
    overflow-x: hidden;
}