h1 {

margin-bottom: 2em;
font-size: 28px;

}

h2 {

margin-bottom: 0.5em;
font-size: 24px;

}

graph {

width: 960px;
height: 500px;
border: 1px solid #ccc;
margin-bottom: 2em;

}

.node {

stroke: #fff;
stroke-width: 1.5px;

}

.link {

stroke: #999;
stroke-opacity: .6;
stroke-width: 1px;

}