So I'm trying to modify the artifact preview thumbnails, i.e. size, padding, border, border color, on Mirage 2 and I can't seem to find the particular file to modify.
Quite simply i'm trying to get this: Current
To look like this: Eventual
Thumbnail styling is defined in these scss files.
These files are compiled into the main.css in the Mirage2 build.
In your source directory, create a file _style.css in dspace\modules\xmlui-mirage2\src\main\webapp\themes\Mirage2\styles and add your overrides there.
See https://wiki.duraspace.org/display/DSDOC5x/Mirage+2+Configuration+and+Customization#Mirage2ConfigurationandCustomization-Simplestylingcustomization for more information.