* Fix#1522: fix attribute error if css is str
* Revert "Fix #1522: fix attribute error if css is str"
This reverts commit b22a77f35a.
* Use `css_tag` only for standard CSS files from Sphinx
... and keep using the custom `link` HTML tag for CSS files included via the
HTML theme option `extra_css_files`.
* Normalize template variables
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Co-authored-by: Manuel Kaufmann <humitos@gmail.com>
Co-authored-by: Anthony Johnson <aj@ohess.org>