Here is the full list of all 8 Super Markup Man achievements.
Play Free Play for 30 minutes.
Complete a level in co-op.
In Free Play, download a file that has a bug in it.
Complete CSS Mode.
Enable "bugs" and squash 50 of them while you play.
Solve HTML Level 6 two different ways.
Solve a CSS level in two moves.
Complete HTML Mode.