diff --git a/resources.whatwg.org/standard-shared-with-dev.css b/resources.whatwg.org/standard-shared-with-dev.css
index 83aa95e1e..62cd27ad9 100644
--- a/resources.whatwg.org/standard-shared-with-dev.css
+++ b/resources.whatwg.org/standard-shared-with-dev.css
@@ -629,3 +629,13 @@ ul.domTree li:not(:last-child)::after {
   content: '';
   border-width: 0.1em;
 }
+
+/* Just in case, SVGs that aren't explicitly
+   marked as darkmode-aware get a white background,
+   as they might have a transparent background
+   and are assuming they're rendered against white.
+*/
+:is(img, iframe)[src$=".svg"]:not(.darkmode-aware),
+svg:not(.darkmode-aware) {
+  background: white;
+}