Update _custom_variables.scss

Author: supernord

_sass/_custom_variables.scss

@@ -1,2 +1,4 @@
 // Find out which theme variables you can use to fine tune the styling of your website here: https://github.com/ELIXIR-Belgium/elixir-toolkit-theme/blob/main/_sass/_variables.scss
 // Copy paste theme here and change where necessary .
+
+$topnav-bg: #205a86;