是的，你可以做到这一点，没有任何额外的加价。这样写：

.active {
  border: 1px solid red;
  border-bottom: 0;
  width: 80px;
  height: 40px;
  margin: 30px;
  position: relative;
  -moz-border-radius: 5px 5px 0 0;
  -webkit-border-radius: 5px 5px 0 0;
  border-radius: 5px 5px 0 0;
}

.active:after,
.active:before {
  content: '';
  width: 40px;
  height: 30px;
  border: 1px solid red;
  position: absolute;
  bottom: -3px;
  border-top: 0;
}

.active:after {
  border-left: 0;
  -moz-border-radius: 0 0 5px 0;
  -webkit-border-radius: 0 0 5px 0;
  border-radius: 0 0 5px 0;
  left: -41px;
}

.active:before {
  border-right: 0;
  -moz-border-radius: 0 0 0 5px;
  -webkit-border-radius: 0 0 0 5px;
  border-radius: 0 0 0 5px;
  right: -41px;
}

<div class="active">hi</div>

检查此http://jsfiddle.net/p6sGJ/