Click on Advanced and select "trust"..... dialog depends on your Browser Edition.
As you can seen on the message.... your browser is unable to validate against the CA because it is unknown right now. vSphere/ESXi creates a selfsigned cert during installation based on a private VMware CA which is unknown to your browser.
2 Solutions:
- Import the CA/Cert into browser SSL Trust store. When connected to vCenter/VCSA there is a CA Download option in the lower right
- Replace CA/Certs of your vSphere infrastructure against a known one
Regards,
Joerg