diff --git a/_ext/translation_graph.py b/_ext/translation_graph.py
index 76c4a479..58be9326 100644
--- a/_ext/translation_graph.py
+++ b/_ext/translation_graph.py
@@ -143,12 +143,14 @@ def run(self):
         )
         # Create figure
         fig = go.Figure(data=heatmap)
+
+        # plotly only lets us use css variables for colors in some places,
+        # and plotly otherwise inlines a lot of CSS itself.
+        # so colors are partially specified here, and partially (forcefully)
+        # overridden in _static/pyos.css
         fig.update_layout(
             paper_bgcolor="rgba(0,0,0,0)",
             plot_bgcolor="rgba(0,0,0,0)",
-            hoverlabel_bgcolor="var(--bs-body-bg)",
-            hoverlabel_font_color="var(--bs-body-color)",
-            font_color="var(--bs-body-color)",
             margin=dict(l=40, r=40, t=40, b=40),
             xaxis_showgrid=False,
             xaxis_side="top",
diff --git a/_static/pyos.css b/_static/pyos.css
index f40cce43..229d7cf2 100644
--- a/_static/pyos.css
+++ b/_static/pyos.css
@@ -428,6 +428,11 @@ th {
     fill: var(--pst-color-text-base) !important;
   }
 
+  g.hovertext > path:first-child {
+    fill: var(--pst-color-background) !important;
+    stroke: var(--pst-color-border) !important;
+  }
+
   @media (max-width: 540px) {
     g.heatmap-label > text {
       display: none;