using dynamic sub class in the html and js code, give you an example in angular.js:

in html:

<div ng-class = getDivClass(userSetting)></div>

in Controller:

$scope.getDivClass = function(userSetting){
     if(userSetting){
        return "blue";
     }
}

in css :

.blue{
   background-color: blue;
}

The above method is implemented by angular.js. if you want to use jquery or something else, the mechanism is similar.