theme: Adjust calendar popover sizing

- Remove bottom blank space on the right column of the calendar popover
  so that the weather card is bottom-aligned with the clear button on
  the left column.
- Remove top blank space on the left column of the calendar popover so
  that the message list is top-aligned with the today button on the
  right column.
- Adjust .message-list-controls sizing to align with other card-styled
  elements.
- Use regular `spacing` instead of margin for some spacing.

https://gitlab.gnome.org/GNOME/gnome-shell/issues/2088
Closes https://gitlab.gnome.org/GNOME/gnome-shell/issues/2120

data/theme/gnome-shell-sass/widgets/_message-list.scss

@@ -11,7 +11,7 @@
 
 .message-list-sections {
   spacing: $base_spacing;
-  margin: $base_margin * 4; // to account for scrollbar
+  margin: 0 $base_margin * 4; // to account for scrollbar
 }
 
 .message-list-section,
@@ -19,14 +19,11 @@
   spacing: $base_spacing;
 }
 
-.message-list-section-list {
-  &:ltr {padding:0;}
-  &:rtl {padding:0;}
-}
-
 // do-not-disturb + clear button
 .message-list-controls {
-  margin: $base_margin $base_margin*2;
+  margin: ($base_margin * 2) ($base_margin * 4) 0;
+  // NOTE: remove the padding if notification_bubble could remove margin for drop shadow
+  padding: $base_margin;
   spacing: $base_spacing;
 }