You can customize the message by clicking a gearwheel in the upper left corner and filling in the textbox. After clicking on the update button, the web address in the browser will be updated. You can then send this new web address to a friend and they will see your message. If your browser supports it, the web address will automatically be copied to the clipboard. Meaning that you should be able to paste it into any other app without manually copying the web address first.
I have not uploaded the code to Github, but an early prof of concept can be viewed on codepen. You will need to use our web browser if you want to view the code I’m afraid. I’m intending to reuse the code for another project I’m working on and that will publish on Github. So the main code will one day be available on Github.
If you are wondering about the color selection. The hearts are in various shades of purple because that is my wife’s favorite color. She was my intended audience for this project.