css制作三角形，下拉框三角形_html/css

 div { width:0px; height:0px; border-top:20px solid transparent; border-left:20px solid transparent; border-right:20px solid transparent; border-bottom:20px solid green; }

div { width:150px; height:150px; position:relative; margin:50px auto;}div p { border:1px solid #000; width:100px; height:100px;}div span { display:block; width:0px; height:0px; border-top:20px solid transparent; border-left:20px solid transparent; border-right:20px solid transparent; border-bottom:20px solid black; position:absolute; top:-40px; left:0;}div span.blank { border-top:19px solid transparent; border-left:19px solid transparent; border-right:19px solid transparent; border-bottom:19px solid white; top:-37px; left:1px;}