http://www.runoob.com/css/css-pseudo-classes.html
https://github.com/DataTables/Select/blob/master/css/select.dataTables.scss
https://cdn.datatables.net/select/1.2.7/css/select.dataTables.css
这个开源项目里面使用before和after生成checkbox的外观
http://www.runoob.com/css/css-pseudo-classes.html
https://github.com/DataTables/Select/blob/master/css/select.dataTables.scss
https://cdn.datatables.net/select/1.2.7/css/select.dataTables.css
这个开源项目里面使用before和after生成checkbox的外观