Twitter Bootstrap question
I'm still new to development and having a go with Twitter Bootstrap for the first time. Struggling to get my head around some of it, but my (possibly dumb) question is this:
I'm a bit confused by how non-semantic the framework is...at least in the tutorials given on the bootstrap site. How do html5 elements fit into this?
For example, is it ok to turn this....
??? (sorry I cant get the markup to indent on this post!)
And is it bad practice to modify the existing 'bootstrap.css' stylesheet, or should I customize the styles using a separate stylesheet?