Readthedocs не включая тему CSS

Я компилирую Readthedocs локально, используя ниже conf.py, и он отлично работает:

# -*- coding: utf-8 -*-
#
# Configuration file for the Sphinx documentation builder.
#
# This file does only contain a selection of the most common options. For a
# full list see the documentation:
# http://www.sphinx-doc.org/en/master/config

# -- Path setup --------------------------------------------------------------

# If extensions (or modules to document with autodoc) are in another directory,
# add these directories to sys.path here. If the directory is relative to the
# documentation root, use os.path.abspath to make it absolute, like shown here.
#
# import os
# import sys
# sys.path.insert(0, os.path.abspath('.'))


# -- Project information -----------------------------------------------------

project = u'VM Sandbox Documentation'
copyright = u'2018, VM'
author = u'VM'

# The short X.Y version
build = 0
version = '3.2.8'
# The full version, including alpha/beta/rc tags
release = version


# -- General configuration ---------------------------------------------------

# If your documentation needs a minimal Sphinx version, state it here.
#
# needs_sphinx = '1.0'

# Add any Sphinx extension module names here, as strings. They can be
# extensions coming with Sphinx (named 'sphinx.ext.*') or your custom
# ones.
# extensions = [
#    'sphinx.ext.autodoc',
#    'sphinx.ext.doctest',
#]

# Add any paths that contain templates here, relative to this directory.
templates_path = ['_templates']

# The suffix(es) of source filenames.
# You can specify multiple suffix as a list of string:
#
# source_suffix = ['.rst', '.md']
source_suffix = '.rst'

# The master toctree document.
master_doc = 'index'

# The language for content autogenerated by Sphinx. Refer to documentation
# for a list of supported languages.
#
# This is also used if you do content translation via gettext catalogs.
# Usually you set "language" from the command line for these cases.
language = None

# List of patterns, relative to source directory, that match files and
# directories to ignore when looking for source files.
# This pattern also affects html_static_path and html_extra_path .
exclude_patterns = [u'_build', 'Thumbs.db', '.DS_Store']

# The name of the Pygments (syntax highlighting) style to use.
pygments_style = 'sphinx'


# -- Options for HTML output -------------------------------------------------

# The theme to use for HTML and HTML Help pages.  See the documentation for
# a list of builtin themes.
#
html_theme = 'sphinx_rtd_theme'
html_theme_path = ["_themes", ]
html_show_sourcelink = False

def setup(app):
    app.add_stylesheet("css/custom.css")

# Theme options are theme-specific and customize the look and feel of a theme
# further.  For a list of options available for each theme, see the
# documentation.
#
# html_theme_options = {}

# Add any paths that contain custom static files (such as style sheets) here,
# relative to this directory. They are copied after the builtin static files,
# so a file named "default.css" will overwrite the builtin "default.css".
html_static_path = ['_static']

html_favicon = 'favicon.ico'
# html_logo = 'images/btlogo.png'

#html_context = {
#    'css_files': [
#        '_static/theme_overrides.css',  # overrides for wide tables in RTD theme
#        ],
#    }

# Custom sidebar templates, must be a dictionary that maps document names
# to template names.
#
# The default sidebars (for documents that don't match any pattern) are
# defined by theme itself.  Builtin themes are using these templates by
# default: ''['localtoc.html', 'relations.html', 'sourcelink.html',
# 'searchbox.html']''.
#
# html_sidebars = {}


# -- Options for HTMLHelp output ---------------------------------------------

# Output file base name for HTML help builder.
htmlhelp_basename = 'btdocsdoc'


# -- Options for LaTeX output ------------------------------------------------

latex_elements = {
    # The paper size ('letterpaper' or 'a4paper').
    #
    # 'papersize': 'letterpaper',

    # The font size ('10pt', '11pt' or '12pt').
    #
    # 'pointsize': '10pt',

    # Additional stuff for the LaTeX preamble.
    #
    # 'preamble': '',

    # Latex figure (float) alignment
    #
    # 'figure_align': 'htbp',
}

# Grouping the document tree into LaTeX files. List of tuples
# (source start file, target name, title,
#  author, documentclass [howto, manual, or own class]).
latex_documents = [
    (master_doc, 'btdocs.tex', u'btdocs Documentation',
     u'VM', 'manual'),
]


# -- Options for manual page output ------------------------------------------

# One entry per manual page. List of tuples
# (source start file, name, description, authors, manual section).
man_pages = [
    (master_doc, 'btdocs', u'btdocs Documentation',
     [author], 1)
]


# -- Options for Texinfo output ----------------------------------------------

# Grouping the document tree into Texinfo files. List of tuples
# (source start file, target name, title, author,
#  dir menu entry, description, category)
texinfo_documents = [
    (master_doc, 'btdocs', u'btdocs Documentation',
     author, 'btdocs', 'One line description of project.',
     'Miscellaneous'),
]


# -- Options for Epub output -------------------------------------------------

# Bibliographic Dublin Core info.
epub_title = project
epub_author = author
epub_publisher = author
epub_copyright = copyright

# The unique identifier of the text. This can be a ISBN number
# or the project homepage.
#
# epub_identifier = ''

# A unique identification for the text.
#
# epub_uid = ''

# A list of files that should not be packed into the epub file.
epub_exclude_files = ['search.html']


# -- Extension configuration -------------------------------------------------

Однако при импорте проекта в readthedocs.com он не включает тему css:

  <link rel="stylesheet" href="../_static/pygments.css" type="text/css" />
  <link rel="stylesheet" href="../_static/css/custom.css" type="text/css" />
    <link rel="index" title="Index" href="../genindex.html" />
    <link rel="search" title="Search" href="../search.html" />
    <link rel="next" title="Intro to Tutorials" href="introduction.html" />
    <link rel="prev" title="VM Documentation" href="../index.html" /> 

Это "правильная" ссылка css:

  <link rel="stylesheet" href="../../_static/pygments.css" type="text/css" />
  <link rel="stylesheet" href="https://media.readthedocs.org/css/sphinx_rtd_theme.css" type="text/css" />
  <link rel="stylesheet" href="../../_static/css/custom.css" type="text/css" />
    <link rel="index" title="Index" href="../../genindex.html" />
    <link rel="search" title="Search" href="../../search.html" />
    <link rel="next" title="Quick Start" href="0_quickstart.html" />
    <link rel="prev" title="Intro to Tutorials" href="../introduction.html" /> 

Это URL:

https://doctestcsserror.readthedocs.io/en/latest/

Репо здесь:

https://github.com/quanghoc/doctest

Любая идея, что я сделал не так?