Principal menu is so big

Hello, I want to correct the dimension of the main menu frame. As shown in the photo, the frame overflows by encroaching on the main page. The part in red shows the frame. The blue part, the part I want to remove.
Please how to change the height of this frame? What is the CSS code to change it?

Thank you for your answer.
I keep looking for the solution to my problem.

I’ve edited your post to correct the markdown that shows the image

what’s your code? what have you tried?