Question

In SASS, when there is an error, it shows a message at the top of the page in the browser. A sample of it is in the attached image.

That text is not selectable. It is not an image. It does not appear in View Source. It is not visible in Firebug.

How is that error text being rendered?

UPDATE

Thanks to @FluffyJack, I investigated and found that a body:before is used in the CSS file that contains the syntax error. Github is not being cooperative at the moment, but I traced where the error message is rendered from in SASS to vendor/sass/lib/sass/error.rb which contains:

body:before {
  white-space: pre;
  font-family: monospace;
  content: "#{header.gsub('"', '\"').gsub("\n", '\\A ')}"; }
END

Answer 1

I think it’s using a content attribute.

Something like

html:before {
  content: "Syntax error..."
}

Check the css.