Font-Size of Off-Canvas-Menu and one other thing

Hey,

I just finished my website and I think I am really well with GeneratePress now, but I can't change the font-size of the Off-Canvas-Menu. Whatever I change in the Customizer won't be accepted in the final page. It always gets overwritten with font-size: 22px;

This website: https://www.kabinencheck.com

And one other thing (not GeneratePress related):
I created a couple of shortcode with PHP in the functions.php. They all work so far. The only thing that kills me is: When you go to WhatsApp for example and type the URL, it will have a small preview of the shared website. I use a shortcode in the title, but when I share a website it always just shows the shortcode name (in this case [year]). Anyone an idea?