css三角形：css画箭头向下的三角形

.arrow {

position: absolute;

bottom: 0;

left: 50%;

transform: translateX(-50%);

width: 0;

height: 0;

border-style: solid;

border-width: 8px 5px 0 5px;

/* 上、左、下、右 */

border-color: #000 transparent transparent transparent;

}