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Popper.js - Interview Questions
Why is my popper in the wrong location (or not visible at all)?
For the left and top placements, Popper relies on HTML Standards Mode for the computeStyles modifier's adaptive option. A problem will occur in Quirks Mode when the <body> is the popper element's offsetParent, and it's taller than the viewport.
To fix it, use the Standards Mode doctype :
<!DOCTYPE html>
  <!-- ... -->
Additionally, make sure your popper element (tooltip, popover, etc...) CSS doesn't include some positioning styles (such as top, left, right, bottom, and transform) because they could interfere with the Popper positioning logic.