Update first_2d_game C# variables capitalization (#4723)

getting_started/first_2d_game/03.coding_the_player.rst

@@ -37,13 +37,13 @@ Start by declaring the member variables this object will need:
 
     using Godot;
     using System;
-    
+
     public class Player : Area2D
     {
         [Export]
-        public int speed = 400; // How fast the player will move (pixels/sec).
+        public int Speed = 400; // How fast the player will move (pixels/sec).
 
-        public Vector2 screenSize; // Size of the game window.
+        public Vector2 ScreenSize; // Size of the game window.
     }
 
 
@@ -75,7 +75,7 @@ a good time to find the size of the game window:
 
     public override void _Ready()
     {
-        screenSize = GetViewportRect().Size;
+        ScreenSize = GetViewportRect().Size;
     }
 
 Now we can use the ``_process()`` function to define what the player will do.
@@ -147,7 +147,7 @@ which returns ``true`` if it's pressed or ``false`` if it isn't.
 
         if (velocity.Length() > 0)
         {
-            velocity = velocity.Normalized() * speed;
+            velocity = velocity.Normalized() * Speed;
             animatedSprite.Play();
         }
         else
@@ -199,8 +199,8 @@ the ``_process`` function (make sure it's not indented under the `else`):
 
         Position += velocity * delta;
         Position = new Vector2(
-            x: Mathf.Clamp(Position.x, 0, screenSize.x),
-            y: Mathf.Clamp(Position.y, 0, screenSize.y)
+            x: Mathf.Clamp(Position.x, 0, ScreenSize.x),
+            y: Mathf.Clamp(Position.y, 0, ScreenSize.y)
         );