docs - update RTD theme

docs/requirements.txt

@@ -2,4 +2,4 @@ parse_cmake
 sphinx==7.1.2
 docutils==0.18.1
 jinja2==3.1.4
-sphinx_rtd_theme==1.3.0
+sphinx_rtd_theme==3.0.0

docs/source/_static/global.css

@@ -0,0 +1,3 @@
+.version-switch select option {
+  color: black;
+}

docs/source/conf.py

@@ -144,7 +144,8 @@ html_theme = 'sphinx_rtd_theme'
 # further.  For a list of options available for each theme, see the
 # documentation.
 html_theme_options = {
-    'navigation_with_keys': True
+    'navigation_with_keys': True,
+    'flyout_display': 'attached',
 }
 
 # Add any paths that contain custom themes here, relative to this directory.
@@ -181,6 +182,10 @@ html_static_path = [
     '_static'
 ]
 
+html_css_files = [
+    'global.css',
+]
+
 # Add any extra paths that contain custom files (such as robots.txt or
 # .htaccess) here, relative to this directory. These files are copied
 # directly to the root of the documentation.