请各位大佬指点！CSS问class为main的div的高度求解答！

Question

.maindiv{
font-size:14px;
height:12px;
}
.title{
position:absolute;
height:20px;
}
.test{
height:20px;
}
.test2{
visibility:hidden;
}
.test3{
display:none;
}
title