body {
    text-align: center;
    font-family: 'Inter', sans-serif;
    line-height: 1.8em;
    color: #333;
    background-color: #fdfdfd;
}

.book {
    margin-top: 2em;
    border-radius: 8px;
}

.book.book-sm {
    width: 300px;
}

.book.book-md {
    width: 400px;
}

.book.book-lg {
    width: 600px;
}

.download-links {
    margin: 1.5em 0;
}

.download-links a {
	display: inline-block;
	padding: 0.5em 1em;
	border: 1px solid #ddd;
	border-radius: 4px;
	background-color: #f0f0f0;
	color: #333;
	text-decoration: none;
	transition: background-color 0.2s ease-in-out;
	margin-right: 0.5em;
}

.download-links a:hover {
	background-color: #e0e0e0;
	border-color: #ccc;
}

.download-links a i {
	margin-right: 0.4em;
}

.des {
    color: #666;
    font-size: 1.1em;
    width: 600px;
    margin: 0 auto;
    text-align: center;
}

.toc {
    width: 800px;
    text-align: left;
    list-style: none;
    margin: 40px auto;
    padding: 0;
    border: 1px solid #e5e5e5;
    border-radius: 8px;
    overflow: hidden;
    box-shadow: 0 4px 6px rgba(0,0,0,0.1);
}

.toc li {
    padding: 10px 20px;
    border-bottom: 1px solid #e5e5e5;
}

.toc li:last-child {
    border-bottom: none;
}

.toc li:nth-child(2n) {
    background: #f9f9f9;
}

.toc .toc-head {
    font-weight: bold;
    font-size: 1.3em;
    padding: 12px 20px;
    background: #282828;
    color: white;
}

.toc .toc-sub-head {
    font-size: 0.9em;
    text-align: center;
    font-weight: bold;
    color: #555;
    background: #f0f0f0;
}

.back-link {
    position: absolute;
    top: 20px;
    left: 20px;
    text-decoration: none;
    color: #555;
    display: flex;
    align-items: center;
    font-size: 1em;
    padding: 0.5em;
    border-radius: 50%;
    transition: background-color 0.2s ease-in-out;
}

.back-link:hover {
    background-color: #f0f0f0;
}

.back-link svg {
    margin-right: 0;
}

.footer {
    margin: 40px auto;
    padding-top: 20px;
    color: #666;
    line-height: 2em;
}

a {
    color: #4d8cdf;
    text-decoration: none;
}

.footer a:hover, .des a:hover {
    text-decoration: underline;
}

@media (max-width: 800px) {
    .book,
    .book.book-sm,
    .book.book-md,
    .book.book-lg {
        width: 80%;
    }

    .book.book-sm {
        max-width: 300px;
    }

    .book.book-md {
        max-width: 400px;
    }

    .book.book-lg {
        max-width: 600px;
    }

    .download-links a {
        display: block;
        width: 90%;
        margin: 1em auto;
        box-sizing: border-box;
    }

    .des {
        width: 90%;
    }

    .toc {
        width: 90%;
        font-size: 0.9em;
    }

    .toc .toc-head {
        text-align: center;
    }
}