Drawing a square (basic noob question)

[SegFault]

Hi,

I'm trying to draw a red square. I've searched for over an hour and it seems the "backdrop" api was changed in 9.0

Anyway, here is my code:

function HelloWorld() 
  print("Hello, World!"); 
  
  local p = CreateFrame("Frame", nil, self, BackdropTemplateMixin and "BackdropTemplate")
  p:SetWidth(100)
  p:SetHeight(100)
  p:SetBackdrop({backdropColor=CreateColor(1,0,0,1)})
  p:SetBackdropColor(1,0,0,1)
  p:SetPoint("TOPLEFT", 100, -100)
  p:Show()
end

I got some of the code from this thread: https://www.wowinterface.com/forums/...d.php?p=336419

This displays nothing however.

I'd appreciate if someone could please point me in the right direction...