I have a edit form of a task list, i using the content type "Workflow Task (Sharepoint 2013)", it has 2 buttons, one for Aprove and other for Deny.

I need to change the color of the Aprove and Deny button, i have tried with Sharepoint Designer (Doesn't allow me to edit the form, even if I have full control permissions) and i have tried with Content Editor, i put this code inside a script tag:

  function changeColors () {
    documento.getElementById("Status_c15b34c3-ce7d-490a-b133-3f4de8801b76_$DropDownChoice_Aprobado").style.backgroundColor = "green";
  }
  
  document.onload= changeColors();
 

But, it doesn't work, until i fire the event in the develp console

Can someone help me?

I have a edit form of a task list, i am using the content type "Workflow Task (Sharepoint 2013)", it has 2 buttons, one for Approve and other for Deny.

I need to change the color of the Approve and Deny buttons, i have tried with Sharepoint Designer (Doesn't allow me to edit the form, even if I have full control permissions) and i have tried with Content Editor as well using below code inside a script tag:

  function changeColors () {
    documento.getElementById("Status_c15b34c3-ce7d-490a-b133-3f4de8801b76_$DropDownChoice_Aprobado").style.backgroundColor = "green";
  }
  
  document.onload= changeColors();
 

But, it doesn't work until I fire the event in the developer console.

Can someone help me?