Sticky navbar with container being shifted slightly to the left upon modal opened

[vtenfys]

Link to demo: https://jsfiddle.net/techdavid/g89ts0rs/1/

When opening a modal, where the page contains a sticky navbar with a container inside it, the container gets shifted slightly to the left due to the padding being applied to the body element.

The .sticky-top element gets a right-padding of 33px added, however there is also white space to the right of this due to the padding on the body. The .sticky-top element should also have a margin-right of -33px applied to compensate for this.

I think that when PR #18441 was submitted, it maybe wasn't tested with .sticky-top (only .fixed-top) and so this is why the problem is still sometimes occurring. I checked the source of the JS file I'm using and found that it does contain code from this PR.

Edit: checked to confirm the problem is only occurring with sticky-top (not fixed-top).

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Before opening an issue:

• Search for duplicate or closed issues => supposedly fixed in Rewrite Modals.setScrollbar() and Modals.resetScrollbar() to properly handle padding-right of body and fixed elements #18441 but still broken in the latest beta
• Validate and lint any HTML to avoid common problems => done
• Prepare a reduced test case for any bugs => https://jsfiddle.net/techdavid/g89ts0rs/1/
• Read the contributing guidelines => done

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When reporting a bug, include:

• Operating system and version => Windows 10
• Browser and version => Chrome 60
• Reduced test cases and potential fixes using JS Bin => https://jsfiddle.net/techdavid/g89ts0rs/1/

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• As much detail as possible for what we should add and why it's important to Bootstrap
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[vtenfys]

The modal is also shifting position to the left slightly whenever the viewport size changes (e.g. in the jsfiddle, adjust the CSS / preview height).

Edit: moved to a separate issue as #23672