:root {
    --bg: #f8fafc;
    --bg-card: #ffffff;
    --text: #0f172a;
    --text-secondary: #64748b;
    --border: #e2e8f0;
    --primary: #3b82f6;
    --primary-light: #eff6ff;
    --success: #22c55e;
    --warning: #eab308;
    --danger: #ef4444;
    --shadow: 0 1px 3px rgba(0,0,0,0.1);
}

.dark {
    --bg: #0f172a;
    --bg-card: #1e293b;
    --text: #f1f5f9;
    --text-secondary: #94a3b8;
    --border: #334155;
    --primary: #60a5fa;
    --primary-light: #1e3a5f;
    --shadow: 0 1px 3px rgba(0,0,0,0.3);
}

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

body {
    font-family: 'Inter', system-ui, -apple-system, sans-serif;
    background: var(--bg);
    color: var(--text);
    line-height: 1.6;
    min-height: 100vh;
}

.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 20px;
}

/* Navigation */
.navbar {
    background: var(--bg-card);
    border-bottom: 1px solid var(--border);
    position: sticky;
    top: 0;
    z-index: 100;
}

.nav-content {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 20px;
    display: flex;
    align-items: center;
    justify-content: space-between;
    height: 64px;
}

.logo {
    font-size: 1.25rem;
    font-weight: 700;
    color: var(--primary);
}

.nav-links {
    display: flex;
    gap: 4px;
    align-items: center;
}

.nav-link {
    padding: 8px 16px;
    border-radius: 8px;
    text-decoration: none;
    color: var(--text-secondary);
    font-size: 0.875rem;
    font-weight: 500;
    transition: all 0.2s;
    cursor: pointer;
    border: none;
    background: none;
}

.nav-link:hover,
.nav-link.active {
    background: var(--primary-light);
    color: var(--primary);
}

.theme-toggle {
    width: 40px;
    height: 40px;
    border-radius: 8px;
    border: 1px solid var(--border);
    background: var(--bg-card);
    color: var(--text);
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    margin-left: 8px;
}

/* Cards */
.card {
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: 12px;
    padding: 24px;
    margin-bottom: 16px;
    box-shadow: var(--shadow);
}

.card-hover {
    transition: transform 0.2s, box-shadow 0.2s;
    cursor: pointer;
}

.card-hover:hover {
    transform: translateY(-2px);
    box-shadow: 0 10px 25px -5px rgba(0,0,0,0.1);
}

/* Grid */
.grid {
    display: grid;
    gap: 16px;
    margin-bottom: 24px;
}

.grid-2 { grid-template-columns: repeat(2, 1fr); }
.grid-3 { grid-template-columns: repeat(3, 1fr); }
.grid-4 { grid-template-columns: repeat(4, 1fr); }

@media (max-width: 768px) {
    .grid-2, .grid-3, .grid-4 { grid-template-columns: 1fr; }
}

/* Buttons */
.btn {
    padding: 10px 20px;
    border-radius: 8px;
    border: none;
    font-weight: 500;
    cursor: pointer;
    transition: all 0.2s;
    font-size: 0.875rem;
    display: inline-flex;
    align-items: center;
    gap: 8px;
}

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

.btn-primary:hover {
    opacity: 0.9;
}

.btn-secondary {
    background: var(--border);
    color: var(--text);
}

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

/* Form elements */
input, select, textarea {
    padding: 10px 14px;
    border: 1px solid var(--border);
    border-radius: 8px;
    background: var(--bg-card);
    color: var(--text);
    font-size: 0.875rem;
    width: 100%;
}

input:focus, select:focus, textarea:focus {
    outline: 2px solid var(--primary);
    outline-offset: 2px;
}

/* Progress bar */
.progress-bar {
    width: 100%;
    height: 8px;
    background: var(--border);
    border-radius: 4px;
    overflow: hidden;
    margin: 16px 0;
}

.progress-fill {
    height: 100%;
    background: var(--primary);
    border-radius: 4px;
    transition: width 0.3s;
}

/* Test styles */
.question-card {
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: 12px;
    padding: 24px;
    margin-bottom: 16px;
}

.option {
    padding: 16px;
    border: 1px solid var(--border);
    border-radius: 8px;
    margin-bottom: 8px;
    cursor: pointer;
    transition: all 0.2s;
}

.option:hover {
    background: var(--primary-light);
    border-color: var(--primary);
}

.option.selected {
    background: var(--primary-light);
    border-color: var(--primary);
    color: var(--primary);
}

.option.correct {
    background: #dcfce7;
    border-color: var(--success);
    color: #166534;
}

.option.wrong {
    background: #fee2e2;
    border-color: var(--danger);
    color: #991b1b;
}

/* Flashcard */
.flashcard-container {
    perspective: 1000px;
    height: 320px;
    cursor: pointer;
    max-width: 500px;
    margin: 0 auto;
}

.flashcard-inner {
    position: relative;
    width: 100%;
    height: 100%;
    transition: transform 0.6s;
    transform-style: preserve-3d;
}

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

.flashcard-front,
.flashcard-back {
    position: absolute;
    width: 100%;
    height: 100%;
    backface-visibility: hidden;
    border-radius: 16px;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    padding: 32px;
    background: var(--bg-card);
    border: 2px solid var(--border);
    box-shadow: var(--shadow);
}

.flashcard-back {
    transform: rotateY(180deg);
    border-color: var(--primary);
}

/* Grid */
.grid {
    display: grid;
    gap: 16px;
    margin-bottom: 24px;
}

.grid-2 { grid-template-columns: repeat(2, 1fr); }
.grid-3 { grid-template-columns: repeat(3, 1fr); }
.grid-4 { grid-template-columns: repeat(4, 1fr); }

@media (max-width: 768px) {
    .grid-2, .grid-3, .grid-4 { grid-template-columns: 1fr; }
}

.flashcard-inner {
    position: relative;
    width: 100%;
    height: 100%;
    transition: transform 0.6s;
    transform-style: preserve-3d;
}

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

.flashcard-front,
.flashcard-back {
    position: absolute;
    width: 100%;
    height: 100%;
    backface-visibility: hidden;
    border-radius: 16px;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    padding: 32px;
    background: var(--bg-card);
    border: 2px solid var(--border);
}

.flashcard-back {
    transform: rotateY(180deg);
    border-color: var(--primary);
}

/* Table */
table {
    width: 100%;
    border-collapse: collapse;
    background: var(--bg-card);
    border-radius: 12px;
    overflow: hidden;
}

th, td {
    padding: 12px 16px;
    text-align: left;
    border-bottom: 1px solid var(--border);
}

th {
    background: var(--bg);
    font-weight: 600;
    font-size: 0.875rem;
    color: var(--text-secondary);
}

/* Utility */
.text-center { text-align: center; }
.mb-4 { margin-bottom: 16px; }
.mb-6 { margin-bottom: 24px; }
.mt-4 { margin-top: 16px; }
.flex { display: flex; }
.items-center { align-items: center; }
.justify-between { justify-content: space-between; }
.gap-2 { gap: 8px; }
.gap-4 { gap: 16px; }
.hidden { display: none; }

/* Animations */
@keyframes fadeIn {
    from { opacity: 0; transform: translateY(10px); }
    to { opacity: 1; transform: translateY(0); }
}

.fade-in {
    animation: fadeIn 0.3s ease-out;
}

/* Responsive */
@media (max-width: 640px) {
    .container { padding: 12px; }
    .card { padding: 16px; }
    .nav-links { display: none; }
}