Why do I have to addClass or removeClass?
Select the '.arrow-prev' element and use .click() to attach a new event handler
Inside the event handler,
a. Use jQuery to select the '.active-slide' element, and save it in a new variable named currentSlide
b. Select the previous slide using .prev(), and save it in a new variable named prevSlide
c. Fade out currentSlide in 600 milliseconds and remove the 'active-slide' class from it.
d. Fade in prevSlide in 600 milliseconds and add the 'active-slide' class to it
Here in exersice 2c and 2d.
var currentSlide = $('.active-slide');
var prevSlide = currentSlide.prev();