Semantic-Org/Semantic-UI — pull request #1157 by coreyfarrell (2014-10-09 07:25:14+00:00)
Title: 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.