Hi Marek
I was able to log in to your site with the credentials sent by mail.
To reduce the extensive whitespace between the horizontal menu and the breadcrumbs, you might add the following to your custom.css
#container_header {
height: 270px !important;
}
But check if there are no negative consequences! Test!
I saw that you use Google fonts and that you load those directly from Google. That has to be avoided for GDPR (DSGVO) reasons. I have written a post in this forum about Google fonts (
https://www.joomla51.com/forum/google-fonts-status-and-local-delivery). You may find the post and especially the discussion useful. It gives a number of hints how to deliver Google fonts from your own server.
In addition, take a look at the hints from my previous post.
Regards
Rolf