How to override the styles & variables?

Hi, I am trying to override the Open edX default styles to change the appearance, for this, I am using the theme template which is inside the themes folder.
I am able to override the logo & other assets but when I am trying to override the primary color using _variables.scss or styles of specific elements then those are not applying.

Can anyone guide me on how should I override the base theme & styles or different elements?