Why only works on JSfiddle? [duplicate]

Answer 1

You're running a script before the DOM is loaded. Either run the script after, or put it in $(document).ready().

<script type="text/javascript">
  $(document).ready(function() {
    $("#right1, #left3").on("click", function() {
        // This fires when 'right' is pressed on content 1,
        // or 'left' is pressed on content 3. In both cases
        // we want to move to show content 2.
        $("#content-container").css({left: "-100%"});
    });

    $("#left2").on("click", function() {
        // This fires when 'left' is pressed on content 2.
        // We want to move to show content 1.
        $("#content-container").css({left: "0%"});
    });

    $("#right2").on("click", function() {
        // This fires when 'right' is pressed on content 2.
        // We want to move to show content 3.
        $("#content-container").css({left: "-200%"});
    });
 });
</script>