Styling and Restructuring Pages

So im using twenty twelve theme but made a custom page thats 1 column.

Now the problem is while its fairly easy to change the style like colors or borders etc im wanting to change the structure of the page for example in that theme the header displays under the navigation but i want to display the header at the top of the page. so how would i be able to rearrange those elements?

also as a second question, is it possible to completely remove the white body where all the content is and instead have content “blocks” of information.
like this very rough drawing.

[IMG]https://i.imgur.com/YzgnP9c.jpg[/IMG]

actually a third question as well, i know im greedy, but while i have a background i wanted it to be responsive and scale normally id just use:
html, body {
height:100%;
margin:0;
padding:0;
overflow:auto;
background-image:url(../img/backgroundImg.jpg);
background-repeat:no-repeat;
background-position:center center;
background-attachment:fixed;
background-size:cover;
)

but i cant seem to find where to make thats change or whether it will work.

any help is greatly appreciated, thank you.