Camera.main not working in C#

Ok, im having quite the issue here, and I've searched and couldn't find any similar posts. Im following this guide here about object labels for a level selection type thing. I've got this Java code here, and it works perfectly:

var target : Transform; var offset = Vector3.zero; private var cam : Camera; private var thisTransform : Transform;

 function Start () {
     target = GameObject.Find("CubeTest").transform;
     thisTransform = transform;
     cam = Camera.main;
     guiText.text = "test";
     guiText.material.color = Color(0,1,1);
 }

 function Update () {
         thisTransform.position = cam.WorldToViewportPoint(target.position + -1*offset);
 }

But im trying to keep my whole project in C# so this is what I have:

 using UnityEngine;
 using System.Collections;
 
 public class NewBehaviourScript : MonoBehaviour {
 private Transform target;
 public Vector3 offset = Vector3.up;
 public Camera mainCamera;
 private Transform selfTransform;
 
     // Use this for initialization
     void Start () {
         target = GameObject.Find("CubeTest").transform;
         selfTransform = transform;
         mainCamera = Camera.main;
         guiText.text = "test";
         guiText.material.color = Color.green;
     }
     
     // Update is called once per frame
     void Update () {
         selfTransform.position = mainCamera.WorldToViewportPoint(target.position + -1*offset);
     }
 }

For some reason with the C# script, im getting the error "'Camera' does not have a definition for 'main'" which isnt making sense to me, seeing as the Javascript worked just fine.

Can anyone shed any light on this?