Steps to reproduce 1. Visit `https://example.org`. 2. Adjust window size to show Letterboxing padding. 3. Open web console and trigger `alert("hello")`. The greyed out background only covers the right and bottom padding.  This is caused by a combination of `place-content: center` on the `.browserStack` element and `position: absolute` on the `.dialogStack` element. The grey background should probably cover the entire tab area. @donuts, can you confirm what area you want the grey background to cover? /cc @ma1