Change vinyasa - button in heder

Hi Radi,

Where does the color of these buttons change?

That would be in the Additional CSS field in the customizer:

/* online classes menu button */

.main-navigation:not(.slideout-navigation) .main-nav li.online-button a {
  background-color: rgba(178,139,178,1.0);
color: #ffffff;
  border: 0;
  line-height: 40px;
	padding: 0px 24px;
  border-radius: 50px;
  margin-left: 20px;
  transition: all 0.5s ease 0s;
}

.main-navigation:not(.slideout-navigation) .main-nav li.online-button a:hover {
  background-color: rgba(178,139,178,0.8);
color: #ffffff;
  transition: all 0.5s ease 0s;
}

/* studio classes menu button */

.main-navigation:not(.slideout-navigation) .main-nav li.studio-button a {
  background-color: rgba(132,140,183,1.0);
color: #ffffff;
  border: 0;
  line-height: 40px;
	padding: 0px 24px;
  border-radius: 50px;
  margin-left: 30px;
  transition: all 0.5s ease 0s;
}

.main-navigation:not(.slideout-navigation) .main-nav li.studio-button a:hover {
  background-color: rgba(132,140,183,0.8);
color: #ffffff;
  transition: all 0.5s ease 0s;
}

How to add there cusom link?

You can add your own link in the menu builder:
https://www.screencast.com/t/iGn02Dkdi

If an update for the topic comes out and I update it, will I lose the changes made? I use other themes and there is automatically created a child theme, but not here?

These changes will be saved during updates. A child theme is not required with GP.

Let me know if this helps :)

Where does the color of these buttons change?
I found, I understood! thanks!

How to add there cusom link?
I know. But how to put it in the thigh Online Classes
or Studio Classes?
When I create a cusom link, how do I make it CSS like Online Classes and Studio Classes?
I want to replace these two buttons Online Classes
and Studio Classes to put a cusom link leading to a subdomain. Do you understand me?

If an update for the topic comes out and I update it, will I lose the changes made? I use other themes and there is automatically created a child theme, but not here?
Super!

Currently, both - Online Classes and Studio Classes in vinyasa https://generatepress.com/site-library/ lead to internal pages!
I want to direct them to external - subdomains, by registering and logging in.

You can just remove the original menu items and add your own custom links in the menu builder.

Then follow the directions here to make them buttons:
https://docs.generatepress.com/article/adding-buttons-navigation/