SVG CSS marker-start: url(#id) properties break when aggregated

Problem/Motivation

SVG CSS using marker-start: url(#some-id); becomes marker-start:url([$css_base_url]#my-id); when aggregated, breaking the CSS style applied to the SVG element. The url() should remain an id selector, unchanged.

This rewrite is problematic for the following SVG CSS properties: marker-start, marker-mid and marker-end.

Proposed resolution

The drupal_build_css_cache() preg_replace_callback needs modified to accommodate marker-start: url(#my-id); CSS properties in aggregated files.

drupal-7.50 /includes/common.inc, Line 3670

       // Anchor all paths in the CSS with its base URL, ignoring external and absolute paths.
        $data .= preg_replace_callback('/url\(\s*[\'"]?(?![a-z]+:|\/+)([^\'")]+)[\'"]?\s*\)/i', '_drupal_build_css_path', $contents);

I'm not going to attempt to modify that regex. ;)

Remaining tasks

• Needs a patch.
• Check if issue persists in D8.