:root[data-theme="light"] {
    --bg-color: #ffffff;
    --text-color: #333333;
    --card-bg: #f5f5f5;
    --header-bg: #f8f9fa;
    --shadow-color: rgba(0, 0, 0, 0.1);
    --accent-color: #4a90e2;
}

:root[data-theme="dark"] {
    --bg-color: #1a1a1a;
    --text-color: #ffffff;
    --card-bg: #2d2d2d;
    --header-bg: #2d2d2d;
    --shadow-color: rgba(0, 0, 0, 0.3);
    --accent-color: #64b5f6;
}

* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
    transition: background-color 0.3s ease, color 0.3s ease, border-color 0.3s ease, box-shadow 0.3s ease;
}

body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    background-color: var(--bg-color);
    color: var(--text-color);
    line-height: 1.6;
    min-height: 100vh;
}

.theme-switch-wrapper {
    position: fixed;
    top: 20px;
    right: 20px;
    z-index: 100;
}

.theme-switch {
    display: inline-block;
    height: 34px;
    position: relative;
    width: 60px;
}

.theme-switch input {
    display: none;
}

.slider {
    background-color: var(--card-bg);
    bottom: 0;
    cursor: pointer;
    left: 0;
    position: absolute;
    right: 0;
    top: 0;
    transition: .4s;
    border-radius: 34px;
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 0 5px;
}

.slider:before {
    background-color: var(--accent-color);
    bottom: 4px;
    content: "";
    height: 26px;
    left: 4px;
    position: absolute;
    transition: .4s;
    width: 26px;
    border-radius: 50%;
    z-index: 2;
}

.slider .fa-sun {
    color: #f1c40f;
    font-size: 14px;
    margin-left: 5px;
    z-index: 1;
}

.slider .fa-moon {
    color: #f1c40f;
    font-size: 14px;
    margin-right: 5px;
    z-index: 1;
}

input:checked + .slider:before {
    transform: translateX(26px);
}

header {
    background-color: var(--header-bg);
    padding: 4rem 2rem;
    text-align: center;
    box-shadow: 0 2px 10px var(--shadow-color);
}

h1 {
    font-size: 2.5rem;
    margin-bottom: 1rem;
    color: var(--accent-color);
}

.subtitle {
    font-size: 1.2rem;
    opacity: 0.9;
}

main {
    max-width: 1200px;
    margin: 2rem auto;
    padding: 0 1rem;
}

.books-container {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
    gap: 2rem;
    padding: 1rem;
}

.book-card {
    background-color: var(--card-bg);
    border-radius: 10px;
    overflow: hidden;
    box-shadow: 0 4px 6px var(--shadow-color);
    transition: transform 0.3s ease;
}

.book-card:hover {
    transform: translateY(-5px);
}

.book-image {
    width: 100%;
    height: 300px;
    object-fit: cover;
}

.book-info {
    padding: 1.5rem;
}

.book-title {
    font-size: 1.25rem;
    margin-bottom: 0.5rem;
    color: var(--accent-color);
}

.book-author {
    color: var(--text-color);
    opacity: 0.8;
    margin-bottom: 0.5rem;
    font-size: 0.9rem;
}

.book-description {
    font-size: 0.9rem;
    margin-bottom: 1rem;
    opacity: 0.9;
}

.book-link {
    display: inline-block;
    padding: 0.5rem 1rem;
    background-color: var(--accent-color);
    color: white;
    text-decoration: none;
    border-radius: 5px;
    transition: opacity 0.3s;
}

.book-link:hover {
    opacity: 0.9;
}

.loading {
    text-align: center;
    padding: 2rem;
}

.spinner {
    width: 40px;
    height: 40px;
    margin: 0 auto 1rem;
    border: 4px solid var(--card-bg);
    border-top: 4px solid var(--accent-color);
    border-radius: 50%;
    animation: spin 1s linear infinite;
}

@keyframes spin {
    0% { transform: rotate(0deg); }
    100% { transform: rotate(360deg); }
}

footer {
    text-align: center;
    padding: 2rem;
    background-color: var(--header-bg);
    margin-top: 2rem;
}

@media (max-width: 768px) {
    header {
        padding: 2rem 1rem;
    }

    h1 {
        font-size: 2rem;
    }

    .books-container {
        grid-template-columns: 1fr;
    }
}