Shortcut to overlay contact information on iPhone wallpaper

The text is black and on a dark background, one can’t see the name and phone number.

I’ve tried adding “color:white” to the syntax but it does make the text invisible.

Actually, I don’t know CSS or HTML so I was just trying things from a search on the W3C website.

How can I make the text white or have a white background with 50% transparency?

PS: I’ve attached a snapshot of what I try to reproduce with Workflow and that I made with an app that’s not updated anymore unfortunately