Spritesheet gif Thumbnail

[BasVH]

Can anyone help me make a sheet thumbnail look nicer?

I added my first sheet on the Spriters resource, (the "Rank icons" one)

and I'd like to add the red background grid on the background,
so it looks like otacon one.

https://www.spriters-resource.com/playstation_2/mgs2/

[Barack Obama]

The red tiled background is always there, since it's part of the automatically generated sheet icon when you upload your 148x125 preview pic:
https://www.spriters-resource.com/playst.../addsheet/

It only becomes visible when you use transparency on the background colour.