.JTBabs.active:before {
content: '';
position: absolute;
left: 20px;
bottom: 0px;
right: 20px;
border-top: 3px solid red;
}
把要加的下边框的那个元素设置为相对定位
position:relative;
.JTBabs.active:before {
content: '';
position: absolute;
left: 20px;
bottom: 0px;
right: 20px;
border-top: 3px solid red;
}
把要加的下边框的那个元素设置为相对定位
position:relative;