How can I remove the HTML/CSS background-color from the body?

My template has a toggle to switch between light and dark mode.
This also works everywhere, just not in the "body". It says rgb(255,255,255).

The original color is overwritten. "var(--ct-body-bg)"

See grafic

I suspect this is because Form.Color is used to set the color.
Try to set form.Color = clNone

Ok, changing the color worked for the body element.
Now there is another SPAN with background-color = white.
Can I remove that too?

I can only suspect this SPAN comes from your template. If it is your template, it is only via altering the template that something can be changed about this.

No, it doesn't come from the template.
I took over the complete HTML code from the template manually.
The form is derived from a base form. The basic form has no HTML code whatsoever.
There is also no additional HTML code in the body of the project file.
Just the "<meta $(BodyParameters)/>"

The HTML of the form starts with this text:

<!-- START wrapper -->
<div class="wrapper">

I think the SPAN is in every WebCore project, isn't it?

This SPAN is NOT in every TMS WEB Core project.
You can easily verify this by opening many of the demos.
So, if you claim it is TMS WEB Core that generates this SPAN, please provide details how we can reproduce this.

I don't know who creates this code, but in the project.js file you can find the code.

This code is found in the "CreateNewForm" function:
A SPAN is created there and then the background is set to white.

I am not claiming that this is injected through TMS Web Core. But I just don't know why it's there.

I keep searching ...

As I said, I do not know who and why this is generated.
But I would be very interested.

I manage first by deleting the "style" in this SPAN.

procedure TfrmKundeSelect.WebFormDOMContentLoaded(Sender: TObject);
  console.log( document.body.firstElementChild.getAttribute( 'style'));
  document.body.firstElementChild.setAttribute( 'style', '');

It looks to be the SPAN from a secondary form that was created and the color comes from this secondary form.Color property