The previous logic attempted to simplify the process by retrieving the first element of the document root. After the first page this would be incorrect since the previous body element exists in the frame tree until the after the current body completed rendering.

fixes #3570

fixes #3569

This change prevents logic or rendering errors in scenarios where a CSS calc function utilizes a non-existent variable as one of the operands.

ref #3530

fixes #3530

Prior to this change a pseudo-element would not be generated if it's only content was a custom property reference. This is because the frame is generated before styles are applied and the custom property reference is unable to resolve. The lack of content in a pseudo-element precludes frame generation.

Even if a frame is generated, it is not rendered to the page if it has no content. This change modifies the content check to exclude only if there is no content (null) rather than empty ("").

fixes #2775 and #3573

Though not valid per the spec to include whitespace in the non-data portion of the data-URI, browser do perform a similar operation. The whitespace removal is done after initial failure in order to minimize impact on documents with a correcty formatted data-URIs.

fixes #1386