a:link {color: dimgray;}
a:visited {color: gray;}
a:hover {color: blue;}
h1 {text-align: center; width: 60%; margin-left: auto; margin-right: auto;}
h3 {text-align: center;}
body {background-image: url(math_bg2.png);}
div {text-align: center; margin-left: 20%; margin-right: 20%; background-color: rgb(224, 224, 224); height: 100%;}
ul {list-style-type: none; padding-bottom: 30px; margin-left: -35px;}