remove spacing between tags:

div.sidebar li,#searchTags li {margin: initial !important; line-height: initial !important;}

add colors:

.tag-type-character a {color: #0A0 !important;}
.tag-type-artist a {color: #A00 !important;}
.tag-type-copyright a {color: #A0A !important;}

remove border around thumbs:

.thumbnail-preview {border: initial !important; padding: initial !important; background: initial !important;}

The desktop and mobile versions are the same version. It adjusts on the fly based on the width of your browser window. Shrink a desktop browser narrow enough and it'll display the same thing as a phone/tablet does. It's not a bug, that's intended functionality.

I'm not seeing red borders around deleted posts.

Also, some of the fields in Trac posts are tabbed for no apparent reason. Not really a problem, just different.
(They start in the middle of the screen instead of being left-justified.)

We didn't change the layout on the trac, only the main post listing/search...

This works, thanks.
I guess you also need it for each type of tag :
div.sidebar li,.tag-type-artist {margin: initial !important; line-height: initial !important;}
div.sidebar li,.tag-type-copyright {margin: initial !important; line-height: initial !important;}
div.sidebar li,.tag-type-character {margin: initial !important; line-height: initial !important;}

I don't like hat it shows so many fewer images, I've always been fine zooming in, and I still have to zoom because the thumbnails are so small, so not only is there no improvement, it feels like a step backwards.

As a totally trivial remark, the hover color for tags is inconsistent. Regular tags go from blue to dark blue (or light blue when you're viewing a specific image), but e.g. character tags go from green to light purple. Maybe it already was like this before though, never paid much attention to it until now...

But yes, as a desktop only user, I also most definitely prefer scrolling through long pages over clicking through short ones.

Put in a option to force a desktop window size then. This resizing thing is a step backwards for anyone using mobile

The new layout for my phone is terrible
I dont like how narrow it is with only 3 images per row compared the previous 5 per row and makes me have to scrolled more and I can see less images at a time than before
Each page now shows less images and creates more pages
The page counter now stops showing how many pages there are after 3 pages compare to be able to see 11 pages
The search bar and tags now sit on the very top of the now narrow image list instead of being conveniently on the side. Putting the tags seperatly from the images actually removes functionality

I understand how these changes were made to aplease some people who wanted support for thier devices but its just not for everyone. Adding an option to just disable resizing would help the people who don't mind zooming.

The + and - buttons next to tags in the index/post listing/search pages don't do anything, right now.

When I click + or - it puts it in the search box but I have to click search, it's not automatic anymore.