.book-content .h1 { font-size: x-large; text-align: center; margin-top: 18pt; }
.book-content .h2 { font-size: large; text-align: center; margin-top: 12pt; }
.book-content .h3 { font-size: medium; text-align: center; margin-top: 9pt; }
.book-content .h4 { text-align: center; margin-top: 6pt; }