month-cell: move day label to the start of the cell

data/theme/gtk-styles.css

@@ -443,6 +443,10 @@ monthcell label {
     font-size: 0.9rem;
 }
 
+monthcell label.day-label {
+    font-size: 1rem;
+}
+
 monthcell.out-of-month label {
     color: alpha(@theme_fg_color, 0.66);
 }