I used Inspect in Chrome on the hamburger icon (what I used to call a menu icon until I noticed people call it a hamburger icon). It seems to be a type of SVG contraption.
I didn't even know you could do all of this in HTML now:
http://www.w3schools.com/svg/svg_path.asp
I ask because my wife has complained that some web pages now cause her (aging laptop) to overheat and stop working.