I made some tweaks for accessibility by making darker borders on form elements and not using placeholders in the form fields. I guess placeholders are a sticking point for a lot of users.
I think they expected you to use absolute positioning on the phone image, but once it's resized and compressed, it's got a small enough file size that it seems safe and not to mention easier to just set it as a background image and position it bottom center. Just need to give a min-height to the container and it plays well even when resizing the browser window. Perhaps it would have been more performant to recreate the gradient background image as a proper css linear gradient, but again, once it's compressed, it's small enough that a background image is fine. I'm a big fan of moderncss.dev and use a lot of their mark up and style suggestions for accessible form inputs, checkboxes, radio buttons, and buttons in all my starter files.
Thank you so much for linking moderncss.dev, looks like a really good resource! Perfect take on this project for accessibility, and you've executed it well.