 $('.btn0').on('click', function(){     $('.box').removeClass('colour0, colour0, colour0');     $('.box').addClass('colour0'); });  $('.btn0').on('click', function(){     $('.box').removeClass('colour0, colour0, colour0');     $('.box').addClass('colour0'); });  $('.btn0').on('click', function(){     $('.box').removeClass('colour0, colour0, colour0');     $('.box').addClass('colour0'); });   $('.btn0').on('click', function(){     $('.box').removeClass('colour0, colour0, colour0');     $('.box').addClass('colour0'); });  