Making Background Transparent

I am trying to make a makeshift onscreen keyboard for Windows 10 and need the background to be transparent, to make it more convenient for the user (the keys are already transparent). I, however, have no idea how to make the background transparent.

Any help would be greatly appreciated.

I believe that I am essentially looking for an updated version of the code in this thread show below:

using System;
using System.Runtime.InteropServices;
using UnityEngine;

public class TransparentWindow : MonoBehaviour
{
    [SerializeField]
    private Material m_Material;

    private struct MARGINS
    {
        public int cxLeftWidth;
        public int cxRightWidth;
        public int cyTopHeight;
        public int cyBottomHeight;
    }

    [DllImport("user32.dll")]
    private static extern IntPtr GetActiveWindow();

    [DllImport("user32.dll")]
    private static extern int SetWindowLong(IntPtr hWnd, int nIndex, uint dwNewLong);

    [DllImport("user32.dll")]
    static extern bool ShowWindowAsync(IntPtr hWnd, int nCmdShow);

    [DllImport("user32.dll", EntryPoint = "SetLayeredWindowAttributes")]
    static extern int SetLayeredWindowAttributes(IntPtr hwnd, int crKey, byte bAlpha, int dwFlags);

    [DllImport("user32.dll", EntryPoint = "SetWindowPos")]
    private static extern int SetWindowPos(IntPtr hwnd, int hwndInsertAfter, int x, int y, int cx, int cy, int uFlags);

    [DllImport("Dwmapi.dll")]
    private static extern uint DwmExtendFrameIntoClientArea(IntPtr hWnd, ref MARGINS margins);

    const int GWL_STYLE = -16;
    const uint WS_POPUP = 0x80000000;
    const uint WS_VISIBLE = 0x10000000;
    const int HWND_TOPMOST = -1;

    void Start()
    {
 // You really don't want to enable this in the editor, but it works there..

    int fWidth = Screen.width;
    int fHeight = Screen.height;
    var margins = new MARGINS() { cxLeftWidth = -1 };
    var hwnd = GetActiveWindow();

    SetWindowLong(hwnd, GWL_STYLE, WS_POPUP | WS_VISIBLE);

    // Transparent windows with click through
    SetWindowLong(hwnd, -20, 524288 | 32);//GWL_EXSTYLE=-20; WS_EX_LAYERED=524288=&h80000, WS_EX_TRANSPARENT=32=0x00000020L
    SetLayeredWindowAttributes(hwnd, 0, 255, 2);// Transparency=51=20%, LWA_ALPHA=2
    SetWindowPos(hwnd, HWND_TOPMOST, 0, 0, fWidth, fHeight, 32 | 64); //SWP_FRAMECHANGED = 0x0020 (32); //SWP_SHOWWINDOW = 0x0040 (64)
    DwmExtendFrameIntoClientArea(hwnd, ref margins);


    }

    void OnRenderImage(RenderTexture from, RenderTexture to)
    {
        Graphics.Blit(from, to, m_Material);
    }
}

The code given did not work, so I assume that it is outdated. I have no idea how to update it myself, since it is a bit out of my skill set. When I upload the code to Unity, it just says that there are errors in the code and that it is not a valid script. When I open the script, however, no errors appear.

I expect to be able to have a relatively good view of whatever is behind my keyboard, like my desktop, but I actually just see a black plane.

Update: So apparently the error message was caused by my script not having the same name as my class. I spent over 4 hours yesterday trying to fix that error message, and this naming incident was the cause :(. Thanks Ruzihm. Anyway, now that the error message is gone, when I run or build the program, my transparent window material just comes up: a dark pink. I then changed my Unity version back to 2018.2.16f1, with no success. Then I removed the #if !Unity Editor line to get the transparency to work perfectly in the editor, but not when I build it. Note, click through does work when I build it and when I run it in the editor.

As discovered in the comments, the problem was fixed when the camera's clear flags were set to solid color and the pink transparent window material was replaced a with white transparent material.