That's because you've added the following to your main stylesheet:
Code:
body{
...
margin: 0 200px;
...
}
You'll notice that if you resize the popup window the text will display fine.
While your 200px margin might work for your regular pages, it won't suit your popups because the popups don't need that massive left/right margin you're imposing on your users.
You could use a different method of forcing those margins on your users, or you could add specific margin rules for those popup boxes that require something smaller like 5px.
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