Reset styles before applying to ensure defaults are restored

examples/basic.css

@@ -2,6 +2,7 @@
 
 App > View {
   docks: side=left/1;
+  text: on #20639b;
 }
 
 Widget:hover {
@@ -28,6 +29,10 @@ Widget:hover {
   border: hkey;
 }
 
+#header.-visible {
+  visibility: hidden;
+}
+
 #content {
   text: white on #20639b;
   border-bottom: hkey #0f2b41;

examples/basic.py

@@ -8,6 +8,7 @@ class BasicApp(App):
     def on_load(self):
         """Bind keys here."""
         self.bind("tab", "toggle_class('#sidebar', '-active')")
+        self.bind("a", "toggle_class('#header', '-visible')")
 
     def on_mount(self):
         """Build layout here."""