diff --git a/.gitignore b/.gitignore
index c8f8ee69..d261ebfc 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,7 +1,8 @@
 /*env*/
-.sphinx/venv
+.sphinx/venv/
 .sphinx/warnings.txt
 .sphinx/.wordlist.dic
+.sphinx/.doctrees/
 _build
 .DS_Store
 __pycache__
diff --git a/.sphinx/_static/furo_colors.css b/.sphinx/_static/furo_colors.css
new file mode 100644
index 00000000..ffc36cbc
--- /dev/null
+++ b/.sphinx/_static/furo_colors.css
@@ -0,0 +1,88 @@
+body {
+    --color-code-background: #f8f8f8;
+    --color-code-foreground: black;
+    --font-stack: Ubuntu, -apple-system, Segoe UI, Roboto, Oxygen, Cantarell, Fira Sans, Droid Sans, Helvetica Neue, sans-serif;
+    --font-stack--monospace: Ubuntu Mono, Consolas, Monaco, Courier, monospace;
+    --color-foreground-primary: #111;
+    --color-foreground-secondary: var(--color-foreground-primary);
+    --color-foreground-muted: #333;
+    --color-background-secondary: #FFF;
+    --color-background-hover: #f2f2f2;
+    --color-brand-primary: #111;
+    --color-brand-content: #06C;
+    --color-api-background: #cdcdcd;
+    --color-inline-code-background: rgba(0,0,0,.03);
+    --color-sidebar-link-text: #111;
+    --color-sidebar-item-background--current: #ebebeb;
+    --color-sidebar-item-background--hover: #f2f2f2;
+    --toc-font-size: var(--font-size--small);
+    --color-admonition-title-background--note: var(--color-background-primary);
+    --color-admonition-title-background--tip: var(--color-background-primary);
+    --color-admonition-title-background--important: var(--color-background-primary);
+    --color-admonition-title-background--caution: var(--color-background-primary);
+    --color-admonition-title--note: #24598F;
+    --color-admonition-title--tip: #24598F;
+    --color-admonition-title--important: #C7162B;
+    --color-admonition-title--caution: #F99B11;
+    --color-highlighted-background: #EbEbEb;
+    --color-link-underline: var(--color-background-primary);
+    --color-link-underline--hover: var(--color-background-primary);
+    --color-version-popup: #772953;
+}
+
+@media not print {
+    body[data-theme="dark"] {
+        --color-code-background: #202020;
+        --color-code-foreground: #d0d0d0;
+        --color-foreground-secondary: var(--color-foreground-primary);
+        --color-foreground-muted: #CDCDCD;
+        --color-background-secondary: var(--color-background-primary);
+        --color-background-hover: #666;
+        --color-brand-primary: #fff;
+        --color-brand-content: #06C;
+        --color-sidebar-link-text: #f7f7f7;
+        --color-sidebar-item-background--current: #666;
+        --color-sidebar-item-background--hover: #333;
+        --color-admonition-background: transparent;
+        --color-admonition-title-background--note: var(--color-background-primary);
+        --color-admonition-title-background--tip: var(--color-background-primary);
+        --color-admonition-title-background--important: var(--color-background-primary);
+        --color-admonition-title-background--caution: var(--color-background-primary);
+        --color-admonition-title--note: #24598F;
+        --color-admonition-title--tip: #24598F;
+        --color-admonition-title--important: #C7162B;
+        --color-admonition-title--caution: #F99B11;
+        --color-highlighted-background: #666;
+        --color-link-underline: var(--color-background-primary);
+        --color-link-underline--hover: var(--color-background-primary);
+        --color-version-popup: #F29879;
+    }
+    @media (prefers-color-scheme: dark) {
+        body:not([data-theme="light"]) {
+            --color-code-background: #202020;
+            --color-code-foreground: #d0d0d0;
+            --color-foreground-secondary: var(--color-foreground-primary);
+            --color-foreground-muted: #CDCDCD;
+            --color-background-secondary: var(--color-background-primary);
+            --color-background-hover: #666;
+            --color-brand-primary: #fff;
+            --color-brand-content: #06C;
+            --color-sidebar-link-text: #f7f7f7;
+            --color-sidebar-item-background--current: #666;
+            --color-sidebar-item-background--hover: #333;
+            --color-admonition-background: transparent;
+            --color-admonition-title-background--note: var(--color-background-primary);
+            --color-admonition-title-background--tip: var(--color-background-primary);
+            --color-admonition-title-background--important: var(--color-background-primary);
+            --color-admonition-title-background--caution: var(--color-background-primary);
+            --color-admonition-title--note: #24598F;
+            --color-admonition-title--tip: #24598F;
+            --color-admonition-title--important: #C7162B;
+            --color-admonition-title--caution: #F99B11;
+            --color-highlighted-background: #666;
+            --color-link-underline: var(--color-background-primary);
+            --color-link-underline--hover: var(--color-background-primary);
+            --color-version-popup: #F29879;
+        }
+    }
+}
diff --git a/.sphinx/_templates/base.html b/.sphinx/_templates/base.html
index 62ffe6b8..33081547 100644
--- a/.sphinx/_templates/base.html
+++ b/.sphinx/_templates/base.html
@@ -5,3 +5,8 @@
   const github_url = "{{ github_url }}";
 </script>
 {% endblock theme_scripts %}
+
+{# ru-fu: don't include the color variables from the conf.py file, but use a
+   separate CSS file to save space #}
+{% block theme_styles %}
+{% endblock theme_styles %}
diff --git a/Makefile b/Makefile
index 4e50d854..b5454dfc 100644
--- a/Makefile
+++ b/Makefile
@@ -3,7 +3,7 @@
 
 # You can set these variables from the command line, and also
 # from the environment for the first two.
-SPHINXOPTS    ?=
+SPHINXOPTS    ?= -c . -d .sphinx/.doctrees
 SPHINXBUILD   ?= sphinx-build
 SPHINXDIR     = .sphinx
 SOURCEDIR     = .
@@ -59,21 +59,22 @@ install: $(VENVDIR) woke-install
 
 
 run: install
-	. $(VENV); sphinx-autobuild -c . -b dirhtml "$(SOURCEDIR)" "$(BUILDDIR)"
+	. $(VENV); sphinx-autobuild -b dirhtml "$(SOURCEDIR)" "$(BUILDDIR)" \
+	$(SPHINXOPTS)
 
 .PHONY: run
 
 # Doesn't depend on $(BUILDDIR) to rebuild properly at every run.
 html: install
-	. $(VENV); $(SPHINXBUILD) -c . -b dirhtml "$(SOURCEDIR)" "$(BUILDDIR)" \
-        -w .sphinx/warnings.txt
+	. $(VENV); $(SPHINXBUILD) -b dirhtml "$(SOURCEDIR)" "$(BUILDDIR)" \
+        -w .sphinx/warnings.txt $(SPHINXOPTS)
 
 .PHONY: html
 
 
 epub: install
-	. $(VENV); $(SPHINXBUILD) -c . -b epub "$(SOURCEDIR)" "$(BUILDDIR)" \
-        -w .sphinx/warnings.txt
+	. $(VENV); $(SPHINXBUILD) -b epub "$(SOURCEDIR)" "$(BUILDDIR)" \
+        -w .sphinx/warnings.txt $(SPHINXOPTS)
 
 .PHONY: epub
 
@@ -88,6 +89,7 @@ clean: clean-doc
 	@test ! -e "$(VENVDIR)" -o \
         -d "$(VENVDIR)" -a "$(abspath $(VENVDIR))" != "$(VENVDIR)"
 	rm -rf $(VENVDIR)
+	rm -rf .sphinx/.doctrees
 
 .PHONY: clean
 
@@ -105,7 +107,8 @@ spelling: html
 
 
 linkcheck: install
-	. $(VENV) ; $(SPHINXBUILD) -c . -b linkcheck  "$(SOURCEDIR)" "$(BUILDDIR)"
+	. $(VENV) ; $(SPHINXBUILD) -b linkcheck "$(SOURCEDIR)" "$(BUILDDIR)" \
+	$(SPHINXOPTS)
 
 .PHONY: linkcheck
 
diff --git a/conf.py b/conf.py
index d7ec4405..a2f1d6ad 100644
--- a/conf.py
+++ b/conf.py
@@ -107,61 +107,6 @@
 html_theme = 'furo'
 html_last_updated_fmt = ''
 html_permalinks_icon = '¶'
-html_theme_options = {
-    'light_css_variables': {
-        'font-stack': 'Ubuntu, -apple-system, Segoe UI, Roboto, Oxygen, Cantarell, Fira Sans, Droid Sans, Helvetica Neue, sans-serif',
-        'font-stack--monospace': 'Ubuntu Mono, Consolas, Monaco, Courier, monospace',
-        'color-foreground-primary': '#111',
-        'color-foreground-secondary': 'var(--color-foreground-primary)',
-        'color-foreground-muted': '#333',
-        'color-background-secondary': '#FFF',
-        'color-background-hover': '#f2f2f2',
-        'color-brand-primary': '#111',
-        'color-brand-content': '#06C',
-        'color-api-background': '#cdcdcd',
-        'color-inline-code-background': 'rgba(0,0,0,.03)',
-        'color-sidebar-link-text': '#111',
-        'color-sidebar-item-background--current': '#ebebeb',
-        'color-sidebar-item-background--hover': '#f2f2f2',
-        'toc-font-size': 'var(--font-size--small)',
-        'color-admonition-title-background--note': 'var(--color-background-primary)',
-        'color-admonition-title-background--tip': 'var(--color-background-primary)',
-        'color-admonition-title-background--important': 'var(--color-background-primary)',
-        'color-admonition-title-background--caution': 'var(--color-background-primary)',
-        'color-admonition-title--note': '#24598F',
-        'color-admonition-title--tip': '#24598F',
-        'color-admonition-title--important': '#C7162B',
-        'color-admonition-title--caution': '#F99B11',
-        'color-highlighted-background': '#EbEbEb',
-        'color-link-underline': 'var(--color-background-primary)',
-        'color-link-underline--hover': 'var(--color-background-primary)',
-        'color-version-popup': '#772953'
-    },
-    'dark_css_variables': {
-        'color-foreground-secondary': 'var(--color-foreground-primary)',
-        'color-foreground-muted': '#CDCDCD',
-        'color-background-secondary': 'var(--color-background-primary)',
-        'color-background-hover': '#666',
-        'color-brand-primary': '#fff',
-        'color-brand-content': '#06C',
-        'color-sidebar-link-text': '#f7f7f7',
-        'color-sidebar-item-background--current': '#666',
-        'color-sidebar-item-background--hover': '#333',
-        'color-admonition-background': 'transparent',
-        'color-admonition-title-background--note': 'var(--color-background-primary)',
-        'color-admonition-title-background--tip': 'var(--color-background-primary)',
-        'color-admonition-title-background--important': 'var(--color-background-primary)',
-        'color-admonition-title-background--caution': 'var(--color-background-primary)',
-        'color-admonition-title--note': '#24598F',
-        'color-admonition-title--tip': '#24598F',
-        'color-admonition-title--important': '#C7162B',
-        'color-admonition-title--caution': '#F99B11',
-        'color-highlighted-background': '#666',
-        'color-link-underline': 'var(--color-background-primary)',
-        'color-link-underline--hover': 'var(--color-background-primary)',
-        'color-version-popup': '#F29879'
-    },
-}
 
 ############################################################
 ### Additional files
@@ -173,6 +118,7 @@
     'custom.css',
     'header.css',
     'github_issue_links.css',
+    'furo_colors.css'
 ]
 html_css_files.extend(custom_html_css_files)