LexX, can you describe what you were doing at the time and the browser you use? The fixed header is supposed to hide itself automatically if you zoom in on an image, and while zoomed, the scroll should be locked so the header doesn’t appear and block the X. The only bug I’ve seen is that if you zoom an image and then resize your browser window, the header reappears, blocking the X.
I think I can fix that though. Binding the escape key is also a good idea.