While mouse is pressed and moved to a button, button should be pressed as well

My problem: If I were to hold my mouse button down on a random area and then move it to a button, the button should be held down as well.

This is the code for when a button is pressed or held down:

 public class downL : Button{
 
 protected KnightControlScript knight;
 
 
 void Start () {
     knight = FindObjectOfType<KnightControlScript> ();
 }
 
 
 public void Update()
 {
     if(IsPressed())
     {
         WhilePressed();
     }
 }
 
 
 public void WhilePressed()
 {
     knight.moving (-1);

 }
 

}

This is the code for when I'm holding the mouse button down on a random position and moving it to a button:

 public class dragLeft : MonoBehaviour, IPointerEnterHandler
 {
 private KnightControlScript knight;
 
 void Start () {
     knight = FindObjectOfType<KnightControlScript> ();
     
 }
 
 // Update is called once per frame
 void Update ()
 {
     
 }
 
 public void OnPointerEnter (PointerEventData eventData){
     
     if(Input.GetMouseButton(0))
         knight.moving (-1);
 }

 }

The problem with the code is that when I hold down my mouse button on a random position and moving it to a button, it only executes the button once, like a single press, even though my mouse button is held down, the button should be held down as well. Any help is appreciated!