Chart background on dark theme

lib/ui/toolbar.dart

@@ -58,6 +58,25 @@ class Toolbar extends StatelessWidget {
               icon: const Icon(Icons.fit_screen),
               label: const Text('Reset view'),
             ),
+            const SizedBox(width: 6),
+            ValueListenableBuilder<bool>(
+              valueListenable: scope.session.cursorEnabled,
+              builder: (_, on, __) {
+                final scheme = Theme.of(context).colorScheme;
+                return OutlinedButton.icon(
+                  onPressed: () =>
+                      scope.session.cursorEnabled.value = !on,
+                  icon: const Icon(Icons.my_location),
+                  label: const Text('Cursor'),
+                  style: on
+                      ? OutlinedButton.styleFrom(
+                          backgroundColor: scheme.primaryContainer,
+                          foregroundColor: scheme.onPrimaryContainer,
+                        )
+                      : null,
+                );
+              },
+            ),
             const _Sep(),
             OutlinedButton.icon(
               onPressed: () => showDialog<void>(