你可以试试这样的 - DEMO
div {
width: 50px;
height: 100px;
position: relative;
margin: 100px;
background: -webkit-linear-gradient(top, #1e5799 0%,#2989d8 100%);
background: -moz-linear-gradient(top, #1e5799 0%, #2989d8 100%);
}
div:after {
z-index: -1;
content: "";
display: block;
position: absolute;
left: -125px;
top: -51px;
margin: 100px;
height: 100px;
width: 100px;
background: #c00;
-webkit-transform:rotate( -45deg );
-moz-transform:rotate( -45deg );
transform:rotate( -45deg );
background: -webkit-linear-gradient(45deg, #1e5799 0%, #2989d8 50%, #ffffff 50%, #ffffff 100%);
background: -moz-linear-gradient(45deg, #1e5799 0%, #2989d8 50%, #ffffff 50%, #ffffff 100%);
}