Icon .png needs transparent pixels for Temperature convertor pwa

[mikehoffms]

\Demos\temperature-converter\icon512.png
was
\Demos\pwa-getting-started\icon512.png

See title bars in pngs in:

• Internal preview: https://review.learn.microsoft.com/microsoft-edge/progressive-web-apps/how-to/index?branch=pr-en-us-3476
• External preview: https://github.com/MicrosoftDocs/edge-developer/blob/user/mikehoffms/pwa-sample/microsoft-edge/progressive-web-apps/how-to/index.md

Actual result: White pixels around the icon.

Browser tab:

Title bar of installed pwa (but transparent might have too low contrast):

Windows task bar:

Expect: Pixels around icon should match background color.