diff --git a/book.toml b/book.toml
index 60acad53..c5a99ea3 100644
--- a/book.toml
+++ b/book.toml
@@ -14,6 +14,7 @@ class = "bob"
 [output.html]
 curly-quotes = true
 additional-js = ["ga4.js"]
+additional-css = ["svgbob.css"]
 git-repository-url = "https://github.com/google/comprehensive-rust"
 edit-url-template = "https://github.com/google/comprehensive-rust/edit/main/{path}"
 
diff --git a/svgbob.css b/svgbob.css
new file mode 100644
index 00000000..2cfc44d7
--- /dev/null
+++ b/svgbob.css
@@ -0,0 +1,4 @@
+/* Ensure text is legible in all themes. */
+svg text {
+  fill: var(--fg);
+}