Bold attribute not working in server side

I am looping inside drop down list but the bold is not applying
  foreach (ListItem li in drpCities.Items)         {             //Check if value is equal to zero             if (li.Value == "0")             {                 //Apply a background color to dropdownlist                 li.Attributes.Add("style", "background-color:red;color:#FFD700;font-weight: bold;");                                 ...