Move in global/world coordinate

Hi, i will make a topdown shooter, and i have a little problem. Move character will be in WASD and aim will be in mouse, but if i try move mouse, for rotate my character aim, the character move coordinate is changed. I like my character moving in global/world coordinate. Up will be forever up, down will be forever down, etc... But i can not do make this, anybody please help, my code is following:

 using UnityEngine;
 using System.Collections;
 
 public class Player : MonoBehaviour {
     CharacterController controller;
     
     public float speed = 10;
     public float gravity = -0.05f;
     public float rotationSpeed = 400;
     
     private float velocityY;
 
     // Use this for initialization
     void Start () {
         controller = GetComponent<CharacterController>();
     }
     
     // Update is called once per frame
     void Update () {
         velocityY += gravity;
         
         Vector3 rotation = new Vector3(0, Input.GetAxis("Mouse X")*rotationSpeed, 0);
         transform.Rotate(rotation * Time.deltaTime);
         
         Vector3 direction = new Vector3(Input.GetAxis("Horizontal")*speed, velocityY, Input.GetAxis("Vertical")*speed);
         
         direction = transform.TransformDirection(direction);
         
         controller.Move(direction * Time.deltaTime);        
     }
 }

Please, excuse me my english, i'm germany.