code blocks in blogger

Something I've just come across is the formatting of code blocks in blogger:

 here is some code

There are plenty of sites out there with information on how to do this [Dashboard->Design->Template Designer->Advanced->Add CSS], but what they fail to mention is that the CSS is not correctly implemented in blogger's preview pane [Edit Posts->Preview].
I spent ages testing out CSS changes, expecting to see the effect in the Preview pane, but nothing seemed to be working. After some frustration I decided to post anyway, viewed the post and there was the CSS formatting implemented correctly. If only someone had mentioned this sooner...