Form code generates invalid container-background-color CSS property

When designing a subscribe form, I entered a Text block with a border and defined a background color (“#ffdddd”). However, when I view the form in a browser, the background color isn’t applied. Looking at the HTML your plugin generates, I see this CSS rule which applies to the paragraph in question:

#ipcm1 {
    padding: 14px;
    width: 100%;
    border: 1px solid rgb(18, 18, 18);
    container-background-color: #ffdddd;
    border-radius: 9px 9px 9px 9px;
}

In the CSS standard, there doesn’t appear to be any such property as container-background-color, and it doesn’t do anything in the Edge browser, current version.

On the sample page, I’ve corrected this problem for myself by adding custom CSS for the #ipcm1 selector, but I’d appreciate if you’d fix your plugin so this workaround is not necessary.

The page I need help with: [log in to see the link]