:root {
    --bg-color: #f7f9fc;
    --card-bg: #ffffff;
    --text-main: #334155;
    --text-muted: #64748b;
    --primary: #3b82f6;
    --primary-hover: #2563eb;
    --border: #e2e8f0;
    --success: #10b981;
}

body {
    margin: 0;
    padding: 0;
    font-family: 'Inter', sans-serif;
    background-color: var(--bg-color);
    color: var(--text-main);
    line-height: 1.6;
    font-size: 16px;
}

.container {
    max-width: 1000px;
    margin: 0 auto;
    padding: 2rem;
}

header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 2rem;
    padding-bottom: 1rem;
    border-bottom: 2px solid var(--border);
}

header h1 {
    margin: 0;
    font-size: 1.5rem;
    font-weight: 600;
}

header h1 a {
    color: var(--text-main);
    text-decoration: none;
}

.task-list {
    background: var(--card-bg);
    padding: 2rem;
    border-radius: 12px;
    box-shadow: 0 4px 6px -1px rgba(0, 0, 0, 0.05);
}

.task-list h2 {
    margin-top: 0;
    color: var(--text-main);
}

.task-list ul {
    list-style: none;
    padding: 0;
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(200px, 1fr));
    gap: 1rem;
}

.task-list li a {
    display: block;
    padding: 1rem;
    background: var(--bg-color);
    border: 1px solid var(--border);
    border-radius: 8px;
    text-decoration: none;
    color: var(--primary);
    font-weight: 500;
    text-align: center;
    transition: all 0.2s ease;
}

.task-list li a:hover {
    background: var(--primary);
    color: white;
    border-color: var(--primary);
    transform: translateY(-2px);
    box-shadow: 0 4px 12px rgba(59, 130, 246, 0.2);
}

.lesson-content {
    background: var(--card-bg);
    padding: 2.5rem;
    border-radius: 12px;
    box-shadow: 0 4px 6px -1px rgba(0, 0, 0, 0.05);
}

.lesson-content h2 {
    margin-top: 0;
    color: var(--text-main);
    border-bottom: 2px solid var(--border);
    padding-bottom: 0.5rem;
    margin-bottom: 1.5rem;
}

.lesson-content h3 {
    color: var(--text-muted);
    font-size: 1.1rem;
    margin-top: 2rem;
}

.step {
    margin-bottom: 1.5rem;
}

.answer {
    margin-top: 2rem;
    padding: 1.5rem;
    background: #ecfdf5;
    border: 1px solid #a7f3d0;
    border-radius: 8px;
    color: #065f46;
    font-weight: 600;
    font-size: 1.1rem;
}

.math-block {
    overflow-x: auto;
    padding: 1rem 0;
}

.nav-buttons {
    display: flex;
    gap: 1rem;
}

.btn {
    display: inline-block;
    padding: 0.5rem 1rem;
    background-color: var(--primary);
    color: white;
    text-decoration: none;
    border-radius: 6px;
    font-weight: 500;
    transition: background-color 0.2s;
    border: 1px solid var(--primary);
}

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

.btn-outline {
    background-color: transparent;
    color: var(--text-main);
    border-color: var(--border);
}

.btn-outline:hover {
    background-color: var(--bg-color);
    color: var(--text-main);
}

footer {
    margin-top: 2rem;
    display: flex;
    justify-content: center;
}

/* Typography elements */
strong {
    color: var(--text-main);
}
hr {
    border: 0;
    height: 1px;
    background: var(--border);
    margin: 2rem 0;
}

.task-statement {
    background: #f8fafc;
    padding: 1.5rem;
    border-radius: 8px;
    border-left: 4px solid var(--primary);
    margin-bottom: 2rem;
    font-size: 1.1rem;
}

.task-statement p {
    margin-top: 0;
    line-height: 2.5;
}

.task-statement .options {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 1rem;
    margin-top: 1rem;
    font-weight: 500;
}