Hello Sitepoint!

I made this site about a year ago with some help from the Sitepoint users (ip Stomme Poes). The site looks great, allthough there were some issues getting it good crossbrowser. The site looks absolutely fine on ie, safari, chrome and firefox. I get however remarks from other people saying the doesn't display all that great on mobile devices and tabs. I'm currently fixing the header issues, but overall, CAN this site be better designed for ipads and stuff? With the design and css it is done now, can we change anything to make it more smartphone-friendly?
Or is this the best we can get it?
This is something which disturbs me a lot, can we make basic websites with a few adjustments smartphone-friendly? Or should we rewrite the whole design? CSS?

Here you can find the site: www.mira-zele.be
I also added the css: Css Mira.txt

I'm not asking you guys to rewrite the whole thing, just to give me some advice on this website if it CAN be done, how to begin, if it's too much work?

Thanks a lot!

Kind regards