伪类选择器 before 和after的使用 实例 制作圆角

比如：

.panel-czbk > .panel-heading::before,.panel-czbk > .panel-heading::after {  content: ' ';  width: 16px;  height: 16px;  border-radius: 8px;  background-color: #f0f0f0;  position: absolute;}.panel-czbk > .panel-heading::before {  top: -8px;  left: -8px;}.panel-czbk > .panel-heading::after {  bottom: -8px;  left: -8px;  box-shadow: 0 2px 1px #ccc inset;}