Creating A Triangle Div With Css

I have recently learned how to create the appearance of a triangle div with CSS and HTML. Now, I would like to know if it is at all possible to add a border around any of the sides

Solution 1:

This is the typical way to do it:

JSFiddle

.arrow-up:after {
    position:absolute;
    content:"";
    width: 0;
    height: 0;
    margin-top:1px;
    margin-left:2px;
    border-left: 10px solid transparent;
    border-right: 10px solid transparent;
    border-bottom: 10px solid white;
}

.arrow-up:before {
    position:absolute;
    content:"";
    width: 0;
    height: 0;
    border-left: 12px solid transparent;
    border-right: 12px solid transparent;
    border-bottom: 12px solid black;
}