Use ControlNet if you want to put something specific into the image.

Also, this Lora is very helpful, just adjust its weight.

Prompt:

(letter B) (favicon:1.3), circle, high contrast BREAK (sticker), 2d art, no humans, (vector art, illustration), vivid colors, simple, (black background) BREAK 4k, 8k, highres BREAK (masterpiece, best quality) <lora:anime_minimalist_v1:0.3>