Updates to standard themes - Thumbnail Layout

[diamondsw]

Is your feature request related to a problem? Please describe.
Although there are a variety of themes that ship with Shimmie, some of them feel like they could use some updates. For this post I'll be focusing on the Danbooru2 theme, as it is the most generically booru-ish theme (and yes, the one I use).

Describe the solution you'd like
In post thumbnail view, the layout spacing does not adapt to the Board Config "Thumbnailing" size. Everything looks fine at the standard 192x192, but trying to change this (for instance, 256x256 or 512x512) makes the thumbnails larger, but the spacing doesn't change and they just overlap each other. This effectively negates the thumbnail size setting.

Here's a screenshot using the Default theme and 384x384 thumbnails: https://imgur.com/a/UAHYALM

Describe alternatives you've considered
I've tried other themes and browsers, and this seems consistent across all I've tried.

Additional context
This limits the ability to use larger thumbnails, which would be nice as monitors just get bigger.

[diamondsw]

Yes, this addresses the layout, and on proper testing (i.e. clearing caches), it also regenerates thumbnails at the higher resolution. Excellent!