<style> .box{ width: 0; height: 0; border-top: 20px solid transparent; border-left: 20px solid transparent; border-right: 20px solid transparent; border-bottom: 20px solid #ccc; } </style> </head> <body> <div class="box"> </div>
保留一条边的颜色,其余的透明,盒子没有大小