Tips

Hold Option when dragging

Holding the Option Key (Alt) will prevent deselection of the selected element, so you can drag objects which are hidden below other objects.

Hold Shift when adjust Padding or Margin to change all at once

Holding the Shift Key while changing the Padding or Margins will change all properties (i.e. left,top,bottom,right) at once. So if you want 10px on all sides, you can do it in a single mouse movement.

:hover not working in FireFox?

Make sure your pages has a DOCTYPE set.