$('#tag-id').removeAttr('style');
$("#id").css({ 'background-color' : '', 'opacity' : '' });
$(".class").css({ 'background-color' : '', 'opacity' : '' });
//You can remove css by the above.
$("body").removeAttr("style");
$("#id .class").css({ 'background-color' : '' });
/*
As mentioned in the jquery documentation:
Setting the value of a style property to an empty string
removes that property from an element
if it has already been directly applied
e.g. $('#mydiv').css('color', '')
*/
$('.tag-class').removeAttr('style');
$.css("background-color", "");
$("#id").css("background-color","");
$("#id").css("opacity","");