how to add css in innerText

hello I have a function in javascript that generates an error message
But I would like to add css in the error message
for example a yellow background and a red color

 //ciblage
 let btn = document.getElementsByClassName("buttons"); 
 let D = document.getElementsByClassName("div_text");
 let errorMessage = document.createElement("div"); 
 stringLength = document.getElementById('username');
const regex = /\W/;
 errorMessage.id = 'warning';
 D[0].appendChild(errorMessage); 
  stringLength.addEventListener('input', function (evt) {
    if (stringLength.value.length > 10) {
         document.getElementById('warning').innerText = "le nombre          de caractères maximum autorisés est de 10"
      btn[0].disabled = true;
    } 
    
  });

>Solution :

document.getElementById('warning').style.backgroundColor="yellow";
document.getElementById('warning').style.color="red";