SOURCE

<ul>
	<li>1</li>
	<li>2</li>
	<li>3</li>
	<li>4</li>
	<li>5</li>
	<li>6</li>
</ul>

ul {
    list-style: none;
    margin: 0;
    padding: 2px;
    display: block;
    clear: both;
    width: 400px;
}

li {
    /*float: left;*/
    box-sizing: border-box;
    -moz-box-sizing: border-box;
    -webkit-box-sizing: border-box;
    width: 100px;
    height: 100px;
    border: 1px solid #ccc;
    margin-left: -1px;
    margin-top: -1px;
    padding: 8px;
    position: relative;
}

li:hover {
    color: white;
    background-color: blue;
    border: 2px solid blue;
}