<style type="text/css">
.chk_1 {
width: 20px;
height: 20px;
position: absolute;
top: 15px;
left: 10px;
}
.chk_1 + label {
background: #ccc;
width: 20px;
height: 20px;
display: inline-block;
position: absolute;
top: 17px;
left: 12px;
}
.chk_1:checked + label {
background:red;
}
</style>
</head> <body>
<input type="checkbox" id="checkbox_a1" class="chk_1">
<label for="checkbox_a1"></label>
</body>