Resize GUI Button (linked to website) ??

I've tried other scripts found in other answers but I can't seem to get any results, I'm creating an Android AR app (Vuforia) and can't seem to use the following script to adapt the button to it's surroundings, because obviously by changing the orientation it's going to change the screen size;

 function OnGUI() {
 
 if (GUI.Button (new Rect(Screen.width/1.2f,Screen.height/2.4f,Screen.width/9.8f,Screen.height/7.6f),"Visit Our Website!")) { Application.OpenURL("https://www.buhlergroup.com/uk/customerservice") ;} 
 
 }

I'd really appreciate some input, thanks!