Layout and styling have nothing to do with php. They should also have nothing to do with the html that php generates. Presentation is a matter for Cascading Style Sheets , which are really very straightforward to use. Try this tutorial and you will see what I mean.
Now of course you already have a site and so it's too late if it has not been designed for CSS. 😃 But if you are getting into this then you might as well learn how it should be done. You'll also find it makes life so much easier when you seperate style from content - far less html to generate or wade through when working on the php scripts.
Plenty of php tutorials around - you could do worse than start with the ones here. But play with it as Brett sez - it's the truth that we learn from our mistakes, especially wwhen it comes to programming, so the more you play the more you learn.