Make my site cross browser compatible

I have already built out the site in CSS and it is based on an Expression Engine Content Management System. The site looks great on Firefox but horrible on Internet Explorer and I have not even looked at it on other browsers like safari. I need someone to make it look consistent throughout all browsers. For a CSS expert, this should be easy as there are not too many issues. This is a very very small project (I Think) but I need it done quick.