content-box：border和padding不計算入width之內

padding-box：padding計算入width內

border-box：border和padding計算入width之內

??.content-box{
????????box-sizing:content-box;
????????-moz-box-sizing:content-box;
????????width:?100px;
????????height:?100px;
????????padding:?20px;
????????border:?5px?solid?#E6A43F;
????????background:?blue;
????}
????.padding-box{
????????box-sizing:padding-box;
????????-moz-box-sizing:padding-box;
????????width:?100px;
????????height:?100px;
????????padding:?20px;
????????border:?5px?solid?#186645;
????????background:?red;????????????????
????}
????.border-box{
????????box-sizing:border-box;
????????-moz-box-sizing:border-box;
????????width:?100px;
????????height:?100px;
????????padding:?20px;
????????border:?5px?solid?#3DA3EF;
????????background:?yellow;
????}

自行比較吧。