float error with screen.width/height

I'm trying to create two windows, positioned using the screen width and height variables.

Thought I had this down, but i'm getting two errors with this script, i'm not sure what it is, I think it might be the subtractions, but i've tried all sorts to see if something wasn't casting properly as a float, but it all seems to.

If I un comment the lines in the gui function, I get about 14 different errors.. I imagine that's because they rely on the variables.

This is the error, the same twice. [ Assets/Scripts/Equipment.cs(10,44): error CS0236: A field initializer cannot reference the nonstatic field, method, or property `Equipment.windowHeight']

     float windowWidth = (Screen.width / 5f) * 2f;
         
             float windowHeight = (Screen.height / 3f) * 2f;
         
             float heightGap = (Screen.height - windowHeight) / 2f;
         
             float widthGap = (((Screen.width / 2f) - windowWidth) / 2f);
         
             //Rect windowOne = new Rect(widthGap, heightGap, windowWidth, windowHeight);
         
             //Rect windowTwo = new Rect(((Screen.width / 2f) + widthGap), heightGap, windowWidth, windowHeight);
         
             void OnGUI()
             {
         
             //    GUI.Window (1, windowOne, InventoryWindow, "Inventory" );
         
             //    GUI.Window (2, windowTwo, EquipWindow, "Equip" );
         
             }
         
             void InventoryWindow(int windowId){    
             }
         
             void EquipWindow(int windowId){
             }