Just eat protein food, beef and eggs (only egg white) regularly every day.
Also, you should know how to rest when practicing, and you can stop when you have muscle aches, so you don't have to force it, otherwise the effect will be bad.
If you want to thicken your legs, you should do some leg strength exercises, usually alternately. After doing it for a while, your leg muscles will definitely change obviously. If you still feel that you are not up to standard, you can start to carry the weight (that is, lift a barbell frog jump or squat), in short, you can stick to it.
There is also that fat and muscle are two different things. The former is that fat has nothing to do with muscle. Although beef is a good health food, it can only be fat without training.