[kitty] change tab_bar_style to powerline

kitty/kitty.conf

@@ -311,7 +311,10 @@ tab_bar_edge top
 
 #: The margin to the left and right of the tab bar (in pts)
 
-tab_bar_style separator
+# TODO: change this to "separator" if maintainer of kitty agrees with me.
+# see https://github.com/kovidgoyal/kitty/pull/2480
+# fortunately, kitty seems to have built-in powerline character support
+tab_bar_style powerline
 
 #: The tab bar style, can be one of: fade or separator. In the fade
 #: style, each tab's edges fade into the background color, in the
@@ -340,6 +343,8 @@ active_tab_font_style   bold
 # inactive_tab_background #999
 inactive_tab_font_style italic
 
+tab_bar_background #999
+
 #: Tab bar colors and styles
 
 #: }}}