[doc] style the sphinx docs

doc/_static/css/custom.css

@@ -0,0 +1,9 @@
+html{
+    --pst-font-size-base: 17px;
+}
+html[data-theme="light"] {
+    --pst-color-primary: #F7A71E;
+}
+.bd-page-width {
+    max-width: 100rem;  /* default is 88rem */
+}

doc/_templates/article-header-buttons.html

@@ -0,0 +1,25 @@
+{#
+SPDX-FileCopyrightText: 2020 Chris Holdgraf
+
+SPDX-License-Identifier: BSD-3-Clause
+#}
+
+{#
+Copied from: https://github.com/executablebooks/sphinx-book-theme/blob/master/src/sphinx_book_theme/theme/sphinx_book_theme/macros/buttons.html
+to remove the light/dark theme switcher button
+#}
+
+{% from "sphinx_book_theme/macros/buttons.html" import render_funcs with context %}
+
+<div class="article-header-buttons">
+    {%- for button in header_buttons -%}
+    {% set btype = button.get("type") %}
+    {% set bopts = button.copy() %}
+    {% set _ = bopts.pop("type") %}
+    {{ render_funcs[btype](**bopts) }}
+    {%- endfor -%}
+
+    {#- Extra theme buttons #}
+    {% include "search-button.html" %}
+    {% include "toggle-secondary-sidebar.html" %}
+</div>

doc/conf.py.in

@@ -38,14 +38,16 @@ highlight_language = 'c++'
 # -- Options for HTML output -------------------------------------------------
 # https://www.sphinx-doc.org/en/master/usage/configuration.html#options-for-html-output
 
+html_static_path = ['_static']
+html_css_files = ['css/custom.css']
 html_theme = 'sphinx_book_theme'
 html_theme_options = {
     'repository_url': 'https://github.com/ginkgo-project/ginkgo/',
     'use_repository_button': True,
-    'use_fullscreen_button': False,
-    'use_download_button': False
+    'use_fullscreen_button': True,
+    'use_download_button': False,
+    "article_header_end": ["article-header-buttons"]
 }
-html_static_path = ['_static']
 html_logo = '@Ginkgo_SOURCE_DIR@/assets/logo.png'
 html_favicon = '@Ginkgo_SOURCE_DIR@/assets/favicon.ico'
 html_title = f'{project} v{release}'