Modal's show at the wrong position when they are in a dimmer that does not take the full page

Modal's seem to always be positioned based on the full size of the window/document.  If the dimmer is contained in an element with window position "left: 100px; top: 60px; right: 0; bottom: 0", then the modal needs to be centered within those dimensions, not the full window dimensions.

A simple fix I found to this was to switch .ui.modal to use position: absolute.  This seems to work when the modal is contained by a dimmer that takes the full page, or when the dimmer is only part of the page.

One thought I had was that instead of switching .ui.modal to position: absolute, it could be overridden for .ui.dimmer > .ui.modal.