month-view: match UI style of year-view popover

year-view: rename popover class to something more generic

data/theme/gtk-styles.css

@@ -150,25 +150,26 @@ GcalYearView GtkButton {
     border-bottom-width: 0;
 }
 
-GtkPopover.popover-sidebar {
+GtkPopover.events {
     background-color: @theme_bg_color;
     padding: 0;
 }
 
-GtkPopover.popover-sidebar GtkBox {
+GtkPopover.events GtkBox {
     border-top-left-radius: 6px;
     border-top-right-radius: 6px;
 }
 
-GtkPopover.popover-sidebar GtkListBox {
+GtkPopover.events GtkListBox {
+    background-color: @theme_bg_color;
     border-radius: 6px;
 }
 
-GtkPopover.popover-sidebar GtkScrolledWindow {
+GtkPopover.events GtkScrolledWindow {
     border-width: 0;
 }
 
-GtkPopover.popover-sidebar GtkButton {
+GtkPopover.events GtkButton {
     border-radius: 6px;
     border-top-left-radius: 0;
     border-top-right-radius: 0;

data/ui/year-view.ui

@@ -110,7 +110,7 @@
   <object class="GtkPopover" id="popover">
     <property name="relative_to">navigator</property>
     <style>
-      <class name="popover-sidebar" />
+      <class name="events" />
     </style>
     <signal name="closed" handler="popover_closed_cb" object="GcalYearView" swapped="yes" />
   </object>