Set default minimal width of buttons to zero

Even if all margins, padding and borders of buttons are removed the
label inside the buttons may still be padded if they are too short.
Setting the minimal width of buttons to zero fixes this issue.

resources/style.css

@@ -40,6 +40,8 @@ button {
     /* Avoid rounded borders under each button name */
     border: none;
     border-radius: 0;
+    /* https://github.com/Alexays/Waybar/issues/1731 */
+    min-width: 0;
 }
 
 /* https://github.com/Alexays/Waybar/wiki/FAQ#the-workspace-buttons-have-a-strange-hover-effect */