feat: white ruler in dark mode

cafe_app.py

@@ -26,7 +26,7 @@ lambdas = {s: sp.lambdify(inputs, sol[0][s]) for s in solve_for}
 ld_total = sp.lambdify(inputs, sol[0][P1] + sol[0][P2])
 
 
-def make_chart(df: pd.DataFrame) -> alt.Chart:
+def make_chart(df: pd.DataFrame, dark: bool) -> alt.Chart:
     source = df.melt("PT", var_name="species", value_name="y")
 
     # Create a selection that chooses the nearest point & selects based on x-value
@@ -54,10 +54,11 @@ def make_chart(df: pd.DataFrame) -> alt.Chart:
     )
 
     # Draw a rule at the location of the selection
+    rule_color = "white" if dark else "black"
     rules = (
         alt.Chart(source)
         .transform_pivot("species", value="y", groupby=["PT"])
-        .mark_rule(color="black")
+        .mark_rule(color=rule_color)
         .encode(
             x="PT:Q",
             opacity=alt.condition(nearest, alt.value(0.3), alt.value(0)),
@@ -124,7 +125,7 @@ def Page():
 
         # put the results in a dataframe, together with input PT values
         df = pd.DataFrame(dict(PT=PT_values) | {k.name: v for k, v in ans.items()})
-        return make_chart(df)
+        return make_chart(df, dark_effective)
 
     chart = solara.use_memo(update, [vmin.value, vmax.value])