HTTPS not working

I have a problem with magic dns and ssl certificate.
I have setup magic dns and run tailsale cert on my pi but when I try to access it, connection is still unsecure. Is there any additional step that I have to do with the certificate to gain https connection?

tailscale cert will write the public and private keys to files in the current directory.

It doesn’t know how to install those files for the particular server software you’re using, like Caddy or Flask or whatever. You need to move the certificate files into the right place and configure that software to use them.