:root {
    --color-primary: #1a5f7a;
    --color-secondary: #2c3e50;
    --color-accent: #2980b9;
    --color-text-dark: #333;
    --color-text-light: #555;
    --font-family-heading: 'Merriweather', serif;
    --font-family-body: 'Source Sans Pro', sans-serif;
    --transition-speed: 0.3s;
    --border-radius: 8px;
}

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

body {
    font-family: var(--font-family-body);
    font-size: 1.1rem;
    line-height: 1.6;
    background-color: #f4f4f4;
    color: var(--color-text-dark);
}

main {
    max-width: 800px;
    margin: 2rem auto;
    padding: 2rem;
    background-color: #ffffff;
    box-shadow: 0 6px 12px rgba(0, 0, 0, 0.1);
    border-radius: var(--border-radius);
    border: 3px solid #b5b5b5;
}

header {
    text-align: center;
    margin-bottom: 2rem;
    padding-bottom: 1rem;
    border-bottom: 2px solid var(--color-primary);
}

.module-title {
    font-family: var(--font-family-heading);
    color: var(--color-primary);
    font-size: 2rem;
    margin-bottom: 0.5rem;
}

.module-subtitle {
    color: var(--color-text-light);
    font-size: 1.1rem;
}

.exercise-list {
    list-style: none;
}

.exercise-item {
    margin-bottom: 2rem;
    padding: 1.5rem;
    background-color: #f8f9fa;
    border-radius: var(--border-radius);
    border-left: 4px solid var(--color-accent);
    transition: transform var(--transition-speed) ease-in-out;
}

.exercise-item:hover {
    transform: translateX(10px);
}

.exercise-header {
    display: flex;
    align-items: center;
    gap: 1rem;
    margin-bottom: 1rem;
}

.exercise-number {
    background-color: var(--color-accent);
    color: white;
    width: 40px;
    height: 40px;
    display: flex;
    align-items: center;
    justify-content: center;
    border-radius: 50%;
    font-weight: bold;
}

.exercise-title {
    font-family: var(--font-family-heading);
    color: var(--color-secondary);
    font-size: 1.25rem;
    font-weight: bold;
}

.exercise-description {
    color: var(--color-text-light);
    margin-bottom: 1rem;
}

.exercise-actions {
    display: flex;
    gap: 1rem;
}

.button {
    display: inline-block;
    padding: 0.5rem 1rem;
    background-color: var(--color-primary);
    color: white;
    text-decoration: none;
    border-radius: var(--border-radius);
    transition: background-color var(--transition-speed) ease-in-out;
}

.button:hover {
    background-color: var(--color-accent);
}

@media (max-width: 600px) {
    main {
        margin: 1rem;
        padding: 1.5rem;
    }

    .exercise-header {
        flex-direction: column;
        align-items: flex-start;
    }

    .exercise-actions {
        flex-direction: column;
    }

    .button {
        width: 100%;
        text-align: center;
    }
}

@media (prefers-color-scheme: dark) {
    :root {
        --color-background: #121212;
        --color-primary: #4fc3f7;
        --color-secondary: #1e293b;
        --color-accent: #0288d1;
        --color-text-dark: #e0e0e0;
        --color-text-light: #b0bec5;
        --color-white: #1c1c1c;
        --color-border: #3a3a3a;
    }

    body {
        background-color: var(--color-background);
        color: var(--color-text-dark);
    }

    main {
        background-color: var(--color-white);
        color: var(--color-text-light);
        box-shadow: 0 4px 6px rgba(0, 0, 0, 0.4);
        border: 3px solid var(--color-border);
    }

    .exercise-item {
        background-color: #1c1c1c;
        border-left: 4px solid var(--color-accent);
    }

    .exercise-title {
        color: var(--color-primary);
    }
}