bootstrap模态框如何加滚动条

 .modal-dialog {
 position: absolute;
 top: 0;
 bottom: 0;
 left: 0;
 right: 0;
 }
 
 .modal-content {
 /*overflow-y: scroll; */
 position: absolute;
 top: 0;
 bottom: 0;
 width: 100%;
 }
 
 .modal-body {
 overflow-y: scroll;
 position: absolute;
 top: 55px;
 bottom: 65px;
 width: 100%;
 }
 
 .modal-header .close {margin-right: 15px;}
 
 .modal-footer {
 position: absolute;
 width: 100%;
 bottom: 0;
 }