Changing CSS based on the value

Answer 1

Here .slice will remove the % sign in this code and the rest of the code will compare the value and assign or remove class

var sdlyvar = $('#sdlyvar').text();   

if (sdlyvar.slice(0,-1) < 0){
    $('#sdlyvar').removeClass("fa-level-up");
    $('#sdlyvar').addClass("fa-level-down");
} else {
    $('#sdlyvar').removeClass("fa-level-down");
    $('#sdlyvar').addClass("fa-level-up");
}