用纯CSS改变html radio/checkbox默认背景颜色样式

checkbox/ radoi默认不支持更改背景颜色，这里可以使用伪类来实现。基本原理是利用after/ before插入新的元素。然后利用新元素的背景颜色或背景图片覆盖掉原来的样式。

input[type=checkbox] {
margin-right: 5px;
cursor: pointer;
font-size: 14px;
width: 15px;
height: 12px;
position: relative;
}

input[type=checkbox]:after {
position: absolute;
width: 10px;
height: 15px;
top: 0;
content: " ";
background-color: #ff0000;
color: #fff;
display: inline-block;
visibility: visible;
padding: 0px 3px;
border-radius: 3px;
}

input[type=checkbox]:checked:after {
content: "✓";
font-size: 12px;
}

input[type=radio] {
margin-right: 5px;
cursor: pointer;
font-size: 14px;
width: 15px;
height: 12px;
position: relative;
}

input[type=radio]:after {
position: absolute;
width: 10px;
height: 15px;
top: 0;
content: " ";
background-color: #ff0000;
color: #fff;
display: inline-block;
visibility: visible;
padding: 0px 3px;
border-radius: 50%;
}

input[type=radio]:checked:before {
content: "✓";
display: block;
position: relative;
top: -2px;
left: 3px;
width: 6px;
height: 6px;
color: #fff;
font-weight: 400;
z-index: 1;
}