For a long time I always forgot the order of the 4 arguments of the margin/padding properties (it's top right bottom left). I always used w3schools to look it up. I use w3schools just to lookup attribute and CSS property names/values etc. It has a nice tree at the left side and concise tables of possible values. If anyone would want to prevent me from using w3schools he/she has to replicate this. It could use some updating and better information about browser support (maybe from a shared source with caniuse.com). I didn't even know that there are tutorials and such on w3schools.