def set_css_prompts(app, config):
    """Set default value for CSS prompt width (optimized for two-digit numbers)."""
    if config.ipysphinx_prompt_width is None:
        config.ipysphinx_prompt_width = {'agogo': '4ex', 'alabaster': '5ex',
            'better': '5ex', 'classic': '4ex', 'cloud': '5ex', 'dotted':
            '5ex', 'guzzle_sphinx_theme': '6ex', 'haiku': '4ex', 'julia':
            '5ex', 'maisie_sphinx_theme': '6ex', 'nature': '5ex', 'pangeo':
            '5ex', 'pyramid': '5ex', 'redcloud': '5ex', 'sizzle': '5.5ex',
            'sphinx_py3doc_enhanced_theme': '6ex', 'sphinx_pyviz_theme':
            '5.5ex', 'sphinx_rtd_theme': '5ex', 'sphinx_typlog_theme':
            '5.5ex', 'traditional': '4ex'}.get(config.html_theme, '7ex')
