This fixes some issues with some specific themes (see).

Some problems are a result of css rules being overwritten by theme rules (astropy-theme, py3doc-enhanced-theme, typlog-theme), others are a result of an old way (julia-theme, pytorch-theme, itcase-theme, pyviz-theme) to include additional javascript files in a theme.

Details concerning javascript issues

The old way to include javascript files (<script type="text/javascript" src="{{ pathto(scriptfile, 1) }}"></script>) does not support a missing file name so the browser tries to fetch a file None, which leaves copybuttonSkipText as undefined and breaks the copy functionality. If a theme uses js_tag to include javascript files for sphinx>=1.8 it works fine (maybe sphinx>=1.8 should also be a minimal requirement for this package?).

If a theme doesn't have the following part (itcase-theme, pyviz-theme):

<script type="text/javascript">
        var DOCUMENTATION_OPTIONS = {
            URL_ROOT:'{{ url_root }}',
            VERSION:'{{ release|e }}',
            COLLAPSE_INDEX:false,
            FILE_SUFFIX:'{{ '' if no_search_suffix else file_suffix }}',
            HAS_SOURCE:  {{ has_source|lower }},
            SOURCELINK_SUFFIX: '{{ sourcelink_suffix }}'
        };
</script>

copybutton.js does throw the following error copybutton.js:105 Uncaught ReferenceError: DOCUMENTATION_OPTIONS is not defined in the console (problem with clipboardButton) and even the icons aren't generated, due to early breaking.

IMHO this should be mentioned in the docs, maybe in a topic like theme support/requirements, so theme creators have a reference , if they want to support sphinx-copybutton