What is the reason for the special treatment of fixed-* and sticky-* elements when the scrollbar disappears during modal.show?

[tesar-tech]

When using a modal, the scrollbar is removed from the body, and padding is added to compensate for the scrollbar width, ensuring the layout remains consistent. This functionality is handled by Bootstrap's scrollbar.js.

However, there is also special treatment for elements with sticky or fixed classes. I’m trying to understand why this is necessary, as everything seems properly aligned with just the padding on the body.

I can’t identify a layout scenario where this special treatment would be required to prevent alignment issues.

Thank you.

[jonhubby]

The special treatment for fixed and sticky elements is to maintain their intended positioning during modal display. When the scrollbar is removed, it can affect how these elements behave, especially if they rely on the viewport height. Adjusting their positioning helps Bootstrap prevent any unexpected shifts or alignment issues. It’s more about preserving the user experience across different layouts.

[tesar-tech]

I get it's for adjusting the positions of elements, but I really cannot came up with an example of such position change. Are there any tests that test such behavior?