How do I apply custom prev and next buttons to slick carousel? I have tried a background image on the
That's because they use an icon font for the buttons. They use "Slick" font as you can see in this image:
Basically, the make the letter "A" the form of an icon, the letter "B" the form of another one and so on.
If you want to know more about icon fonts click here
If you want to change the icons, you need to replace the whole button code or you can go to www.fontastic.me and create your own icon font. After that, replace the font file for the current one and you'll have your own icon.