How do I consistently add an extra CSS file to override the existing stylesheets

[vharsh]

I tried overriding the default colour of the ReadTheDocs theme.
I saw different results

CSS files seen locally

• "_static/css/theme.css"
• "_static/theme_overrides.css"

CSS files seen on ReadTheDocs

• "_static/theme_overrides.css"
  Please suggest a consistent way so that I can add a custom CSS, which is applied both locally & and online.

[Blendify]

Have a look at http://www.sphinx-doc.org/en/stable/extdev/appapi.html#sphinx.application.Sphinx.add_stylesheet

[kiwiroy]

The set css_files from this post on theme modification worked, although adding @import url("//media.readthedocs.org/css/sphinx_rtd_theme.css"); to the top of _static/theme_overrides.css also appeared functional.