box-size

<style>
*{ margin:0; padding:0; list-style:none; font-family:"\5FAE\8F6F\96C5\9ED1";}
.content_box{
    box-sizing:content-box;
    -webkit-box-sizing:content-box;
    width: 100px;
    height: 100px;
    padding: 20px;
    border: 5px solid #E6A43F;
    background: blue;
}
.padding_box{
  box-sizing:padding-box;
        -webkit-box-sizing:padding-box;
        width: 100px;
        height: 100px;
        padding: 20px;
        border: 5px solid #186645;
        background: red; 
}
.border_box{
    box-sizing:border-box;
    -webkit-box-sizing:border-box;
    width: 100px;
    height: 100px;
    padding: 20px;
    border: 5px solid #E6A43F;
    background: green;
}
</style>

火狐下的效果↓

chrome下的效果↓

 

padding-box   只有在火狐下起作用