How can I limit my rotation around an object ?

I've searched for the answer on the forums, but since I couldn't find one that works for me I'll ask again. So I have a camera rotating around an object. I want to limit the rotation to stop when it reaches X degrees of 90 or -90 aka when it looks at it exactly from above or below. I tried to use clamp, tried to set the degrees = 90 with eulerAngles if its above 90 or below -90 and both did not work, it's possible I didn't implement them properly.(Mind that, I clamped at the Start() function shouldn't that work ? ) It's like the camera completely ignores the limit. TL:DR I want to restrict the camera's rotation around an object but Mathf.Clamp and eulerAngles didn't work . Any guesses ? My code looks like this (Start function, variable delcaration etc are skipped) :

 void Update()
 {

     horizontalInput = Input.GetAxis("Horizontal");
     verticalInput = Input.GetAxis("Vertical");
     if (horizontalInput != 0)
     {
         transform.RotateAround(center.position, center.up, -horizontalInput * 90 * Time.deltaTime);
     }
     if (verticalInput != 0)
     {
        
         transform.RotateAround(center.position, transform.right, verticalInput * 90 * Time.deltaTime);

     }
 }