Unnesesary scrollbar showing in primary sidebar

[PawelKorsak]

Describe the bug

context
When I create an almost empty book.

expectation
I expected scrollbar to not be visible.

bug
But instead scrollbar in sidebar is showing.
Example screenshot:

Source Folder: /home/pawel/mab-github/MD80-x-CANdle-Documentation
Config Path: /home/pawel/mab-github/MD80-x-CANdle-Documentation/_config.yml
Output Path: /home/pawel/mab-github/MD80-x-CANdle-Documentation/_build/html
[sphinxcontrib-bibtex] Beware that docutils versions 0.18 and 0.19 (you are running 0.18.1) are known to generate invalid html for citations. If this issue affects you, please use docutils<0.18 (or >=0.20 once released) instead. For more details, see https://sourceforge.net/p/docutils/patches/195/
Running Sphinx v5.0.2
[etoc] Changing master_doc to 'intro'
loading pickled environment... checking bibtex cache... up to date
done
myst v0.18.1: MdParserConfig(commonmark_only=False, gfm_only=False, enable_extensions=['colon_fence', 'dollarmath', 'linkify', 'substitution', 'tasklist'], disable_syntax=[], all_links_external=False, url_schemes=['mailto', 'http', 'https'], ref_domains=None, highlight_code_blocks=True, number_code_blocks=[], title_to_header=False, heading_anchors=None, heading_slug_func=None, footnote_transition=True, words_per_minute=200, sub_delimiters=('{', '}'), linkify_fuzzy_links=True, dmath_allow_labels=True, dmath_allow_space=True, dmath_allow_digits=True, dmath_double_inline=False, update_mathjax=True, mathjax_classes='tex2jax_process|mathjax_process|math|output_area')
myst-nb v0.17.2: NbParserConfig(custom_formats={}, metadata_key='mystnb', cell_metadata_key='mystnb', kernel_rgx_aliases={}, execution_mode='force', execution_cache_path='', execution_excludepatterns=[], execution_timeout=30, execution_in_temp=False, execution_allow_errors=False, execution_raise_on_error=False, execution_show_tb=False, merge_streams=False, render_plugin='default', remove_code_source=False, remove_code_outputs=False, code_prompt_show='Show code cell {type}', code_prompt_hide='Hide code cell {type}', number_source_lines=False, output_stderr='show', render_text_lexer='myst-ansi', render_error_lexer='ipythontb', render_image_options={}, render_figure_options={}, render_markdown_format='commonmark', output_folder='build', append_css=True, metadata_to_fm=False)
Using jupyter-cache at: /home/pawel/mab-github/MD80-x-CANdle-Documentation/_build/.jupyter_cache
WARNING: The default value for `navigation_with_keys` will change to `False` in the next release. If you wish to preserve the old behavior for your site, set `navigation_with_keys=True` in the `html_theme_options` dict in your `conf.py` file.Be aware that `navigation_with_keys = True` has negative accessibility implications:https://github.com/pydata/pydata-sphinx-theme/issues/1492
building [mo]: targets for 0 po files that are out of date
building [html]: targets for 3 source files that are out of date
updating environment: 0 added, 3 changed, 0 removed
reading sources... [100%] intro                                                                                                                                                         
looking for now-outdated files... none found
pickling environment... done
checking consistency... done
preparing documents... done
writing output... [100%] intro                                                                                                                                                          
generating indices... genindex done
writing additional pages... search done
copying images... [100%] images/md80_actuators.jpg                                                                                                                                      
copying static files... done
copying extra files... done
dumping search index in English (code: en)... done
dumping object inventory... done
build succeeded, 1 warning.

The HTML pages are in _build/html.

===============================================================================

Finished generating HTML for book.
Your book's HTML pages are here:
    _build/html/
You can look at your book by opening this file in a browser:
    _build/html/index.html
Or paste this line directly into your browser bar:
    file:///home/pawel/mab-github/MD80-x-CANdle-Documentation/_build/html/index.html            

===============================================================================

problem
This is a problem for people creating documentation because it's distracting and looks out of place.

Reproduce the bug

1. Create book
2. Build it

List your environment

Jupyter Book      : 0.15.1
External ToC      : 0.3.1
MyST-Parser       : 0.18.1
MyST-NB           : 0.17.2
Sphinx Book Theme : 1.0.1
Jupyter-Cache     : 0.6.1
NbClient          : 0.7.4

Python 3.10.12
Mozilla Firefox 119.0
Ubuntu 22.04.3 LTS

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[mikegerber]

We've also encountered this. This seems to be caused by the (invisible) rtd-footer-container div; when I remove the element in Firefox' inspector, the scrollbar goes away.

[mikegerber]

Dupe of #732