我好菜啊，代碼附上，

div{width:?300px;height:?1px;background:?-moz-linear-gradient(right,?#fff,?#0000ff);}
div{width:?300px;height:?1px;background:?-o-linear-gradient(right,?#fff,?#0000ff);}
div{width:?300px;height:?1px;background:?-webkit-linear-gradient(right,?#fff,?#0000ff);}
div{width:?300px;height:?1px;background:?-ms-linear-gradient(right,?#fff,?#0000ff);}

這樣就行了