'Can't get rid of the margin around HTML document

I am using Responsive Signing and I have a HTML document starting the DOM tree like this:

<!DOCTYPE html>
<html>
    <head>
      <meta charset="UTF-8">
    </head>
    <body style="font-family: sans-serif; padding: 0px; margin: 0px; font-size: 12px; padding: 0px; background-color: pink; color: #11263c;">
      My content goes here!
    </body>
</html>

I have tried setting the margin and padding to 0px. I saw some other SO questions related that suggested doing negative values like -2em but still had no success on that.

Any other suggestions? Is this by design? Any way around it? I want my HTML to take up the entire height and width of the document. Thanks.

EDIT: I would like the pink area (representing my content) to stretch to the bounds of the document. Example Image



Solution 1:[1]

This is not currently an option with DocuSign. The PDF has fixed width that cannot currently be modified, even if you use HTML for sending.

Sources

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Source: Stack Overflow

Solution Source
Solution 1 Inbar Gazit