<!DOCTYPE html><htmllang="en"><head><metacharset="UTF-8"><metaname="viewport" content="width=device-width, initial-scale=1.0"><title>画三角形</title><style>
.triggle{
width:0px;
height:0px;
border-width:100px;
border-style: dotted dotted solid dotted;
border-color: transparent transparent red transparent;
}
</style></head><body><divclass="triggle"></div></body></html>
前端小技巧：边框写三角形