CSS Tutorial - Do it Yourself

My first tutorial... I hope it is useful.
Critics or ideas, please send me a note then
And if you create a CSS with this, please, please show me

the CSS helper can be found here

Important
I found two mistakes:
for the top it's .journaltop instead of box and
a:hover instead of a.hover

I'm very sorry for that. If you find more mistakes, please note me, I'm going to fix that!