I'm a beginner in 2D game development and I wanna focus on the logic of the game. It would save a ton of my time if there is any source to download the game resource eg, characters, maps, etc.
I don't want to personally edit the base question based on my own opinion, but a better 'version' of this question could be:
"How can I get right to the programming and logic of my game without working on the sprites and other design aspects?"
As @Jon has mentioned in his comment, the best answer to that is simply colored squares. In fact you probably don't want to spend too much time on sprites and artwork until you've created a working prototype of your idea.
Make it just pretty enough to be playable.