h1, h2 {
    text-align: center;
}

.container {
    position: relative;
    width: 700px;
    height: 520px;
    margin: 0 auto;
}

ul {
    padding-left: 0;
    border: 2px solid black;
}
ul li {
    list-style: none;
    padding-left: 0;
    height: 20px;
    padding: 4px;
    border: 1px solid #000;
    margin-top: -1px;
    background: white;
}
ul.playing li {
    cursor: pointer;
}
ul.playing li:hover {
    background: gray;
}
ul li:first-child, ul li.ui-sortable-helper {
    margin-top: 0;
}

#source, #target {
    position: absolute;
    top: 0;
    height: 493px;
    width: 300px;
}
#source {
    left: 0;
}
#target{
    right: 0;
}
#target.success li {
    background: green;
}

#go-button {
    text-align: center;
}