* {
    box-sizing: border-box;
}

body {
    text-align: center;
}

li {
    list-style: none;
    display: inline-block;
    margin:1em;
    padding:0.5em;
    border-radius:5px;
}

li:hover {
    background-color: silver;
}

em {
    font-weight: 600;
    color: red;
}

li.selected {
    background-color: green;
}