I did not personally discover the 45px value, but when a specific value like this is mentioned it is usually the result of some css debugging done with a tool like Firebug for FireFox. This is a terrific tool that will allow you to inspect objects and page parts on the fly and make adjustments to them. Normally when I see a css issue like this it is the first thing that I will try. I inspect the element then I look at the css that is involved and start making adjustments.