CSS Triangles.
CSS
.arrow-down {
width: 0;
height: 0;
border-left: 20px solid transparent;
border-right: 20px solid transparent;
border-top: 20px solid #f00;
}
HTML
<div class="arrow-down"></div>
Resource
More info can be found here
1
solved How is this specific design effect achieved? [closed]