UnityのEditorについてのエラー

実現したいこと

using UnityEditor;
using UnityEngine;

namespace Umbrella.Utility
{
[CustomEditor(typeof(CameraSizeAdjuster), true)]
public class CameraSizeAdjusterEditor : Editor
{
private SerializedProperty _aspectRatio;
private SerializedProperty _baseCameraSize;
private SerializedProperty _baseCameraFOV;
private SerializedProperty _showBaseAspectArea;
private SerializedProperty _baseAspectAreaColor;

private Camera _camera; private void OnEnable() { _aspectRatio = serializedObject.FindProperty("_baseAspectRatio"); _baseCameraSize = serializedObject.FindProperty("_baseCameraSize"); _baseCameraFOV = serializedObject.FindProperty("_baseCameraFOV"); _showBaseAspectArea = serializedObject.FindProperty("_showBaseAspectArea"); _baseAspectAreaColor = serializedObject.FindProperty("_baseAspectAreaColor"); var adjuster = target as CameraSizeAdjuster; _camera = adjuster.GetComponent<Camera>(); } public override void OnInspectorGUI() { serializedObject.Update(); EditorGUILayout.PropertyField(_aspectRatio); if (_camera.orthographic) { EditorGUILayout.PropertyField(_baseCameraSize); } else { EditorGUILayout.PropertyField(_baseCameraFOV); } EditorGUILayout.PropertyField(_showBaseAspectArea); if (_showBaseAspectArea.boolValue) { EditorGUILayout.PropertyField(_baseAspectAreaColor); } serializedObject.ApplyModifiedProperties(); } }

}

発生している問題・エラーメッセージ

Assets/CameraSizeAdjuster/Editor/CameraSizeAdjusterEditor.cs(7,45): error CS0118: 'Editor' is a namespace but is used like a type