A CodePen by fff. how to draw one triangle with div - draw a triangle only with css+div.

index.haml

.aa
.a
.a.b
.a.b.c
.a.b.c.d
.a.b.c.d.e
.clear
.label "thin boader div"
.label "fat boader div"
.label "div with 3 boaders"
.label2 "0 size div"
.label2 "div with 2 boaders"
.label2 "triangle"

style.css

div{
  display: inline-block;
  margin: 10px;
}

.label{
  width: 100px;
}

.label2{
  width: 80px;
}

.clear{
  display: block;
}

.aa{
  border: black solid 10px;
  height: 80px;
  width: 80px;
}

.a{
  border: black solid 40px;
  height: 20px;
  width: 20px;
}

.b{
  border-right: transparent solid 40px;
}

.c{
  height: 0px;
  width: 0px;
}

.d{
  border-left: transparent solid 40px;
}

.e{
  border-top: transparent solid 40px;
}