 <p>Unicode character <code>U+25BC</code> is a solid triangle pointing down: ▼. You can also finagle html block elements to look like triangles by giving them a width and height of zero and applying special border properties to three of the element's sides. This technique is known as the <a href="http://davidwalsh.name/css-triangles" rel="nofollow">CSS triangle hack</a>.</p>