Changing the Font Size/Style and Buttons Size/Style

I am tasked to change the style and size of the fonts and buttons on yii… since the intended user would be no so technical and old people. please do help me by posting some tutorial or tips on how to change the fonts and buttons size and style. Thanks in advance.

You have to edit the css file in the css folder.

Did you find how to change the style of a button?

Which CSS file/ where in CSS file needs to be changed?

Thank you