Changing CSS based on the value

Answer 1

Use JavaScript parseFloat for parsing percentage (http://www.w3schools.com/jsref/jsref_parsefloat.asp).

var percent = $('#sdlyvar').text();
var result = parseFloat(percent) / 100.0;

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