I have a triangle (JSFiddle) using this CSS:
.triangle { width: 0; height: 0; border-top: 0; border-bottom: 30px solid #666699; border-le
None of the others worked for me, but I found the following did (by accident):
.triangle { border: 1.3rem dashed #666699; border-right: .5rem solid rgba(255, 255, 255, 0); }
The mixture of dashed/solid and the rgba fix worked in FF31, IE11, and Chrome36.