As explained better in text decor, pixels are a great way to make your rentries cuter etc etc. so heres my recommendations on where to find them!
This is gonna be a pretty quick page, search up "favicon" on tumblr, any color if you like and thats every pixel you'll ever need! I personally use /borderpixels & ulzzang on rentry sometimes too ! you can also look on neocities though it's a bit more time-consuming in my opinion.. You can find out how to recolor them on recoloring gifs