Skateside

Start understanding the concepts of object-oriented programming (assuming you don't already). I'm sure backbone has it's uses, never really figured out what they are but then I've never tried building a large application purely in JavaScript.

I guess looking into things like RequireJS, read up on the works of Nicholas Zakas and the people he mentions and unit test everything.

Before anyone answers this, can I just check: is this homework?

Have you tried putting position: relative; on #masthead nav?

 

I'll try reading your post fully first ...

 

Your problem is your clear fix, .container:after, .row:after, this has visibility:hidden on it, causing the :after on #masthead nav to be invisible. Try creating another element around your nav and putting the container class on that.

The only thing I like about the !important rule is that it has a higher specificity than an inline style. That's useful when you have to modify a page, don't control the markup and someone has used inline styles. I feel that at all other times it shouldn't be used.

I don't necessarily agree with that statement.

Classes should be used to style elements that you may have several of on a page such as a small container with the same border/background/dimensions etc.

IDs should be used to style elements that are unique to the page and are not repeated elsewhere.
 
These are their semantic uses. 
But if you follow the semantics correctly then you'll often not need to use IDs anyway such as using <nav> instead of <div id="nav">. I mainly use IDs for elements with Javascript functionality and I only use classed for elements that will be repeated with same styles. CSS Specificity isn't an issue if your code is clean and you work down through each nest.

Just to provide a difference of opinion here, I almost never use IDs any more (even for JavaScript). I prefer using classes because it makes the CSS more modular and easier to work with owing to the smaller specificity. Having read up on SMACSS, I live the idea of sub-classing my modules and that's much harder with IDs.

I'm not saying that IDs are bad things, just that there are those of us out there who chose not to use them.