position: fixed caused element to be wider than browser

Question

Can anyone tell me why position:fixed cause the element to be wider than the browser or other content on the page and causing horizontal scrolling?

Here is the code HTML

Answer 1

Because position:fixed behave as the element is detached from document, and placed in the nearest top/left corner of the document, adding default body's margin. That's why it will take the same amount of space, as your second div, if you reset body margin.