I came across with this bug that our page design doesn't render properly. From the users perspective it might be neglegible 'coz it only dealt with the small line crossing the other section of the page which was not really a big deal - the final look was still good. But not to our architect. 

And so I started checking all the html tags, its styles and everything. All seems fine. I then used Firebug to see what were really rendered in the browser. There I found that some div elements are messed inside other elements which should not be. That suggested that there are some elements that do not have closing tags. Going back to the html markups pointed me to this element:

<div style="clear: both;" />

 It seems fine,right? But it's not. Writing the old right way it should be: 

 <div style="clear: both;" ></div>

 That solved my problem.