When I try to set the size of text in a GUI.Button by changing the width and height in the Rect, the button’s size changes, but not the text’s. What is the problem?

That’s not a problem, that’s expected and desired behavior. If you want to change the size of the text, then change the font size in the GUIStyle or skin, or import the font at a larger size.

You need to change the font size of the GUIStyle for whatever GUI element you’re trying to draw.

   GUI.skin.button.fontSize = 16;

   var someRectangle = Rect(0, 0, 200, 100);

   GUI.Button(someRectangle, "press me");

There’s a lot of good documentation if you google “unity guistyle” or stuff about GUI skins…