change style from a list from js

i’m creating a chat for a website and when i display the mesages i want to change the color when the you are the owner.
i dont know how to make it, because the ul tags get stacked when you add more mesages

btw the style that i want to ass is: style=”background-color: #C9DAE4;”

this is the code

socket.on("postmesage", function (mesage, owner) {
      var div = document.getElementById('chat');
      div.innerHTML += `
      <ul class="list-group list-group-horizontal" id="mesage">
          <li class="list-group-item list-group-item-warning">${mesage.mesage}</li>
          <li class="list-group-item list-group-item-warning" id="mesageowner">${mesage.owner}</li>
      </ul>`;

      if owner === document.getElementById("mesageowner").getAttribute('value')) {
alert("change style")
} 
    });

I have tried to get the mesage owner but it returns null.