javascript - working with Image Slider using JS and css -

i'm working on image slider , copied code site. when i'm reviewing css file, came across selector .sliderinner , i'm having trouble figuring out meaning , function of in #slider div.sliderinner example , if class name,id or class selector defined user; or pseudo class predefined example :hover etc.

i have css file wherein #slider div.sliderinner included/indicated , linked html file in html file, there's no .sliderinner class/id name defined , when tried remove selector #slider div.sliderinner in css file , opened html file, image slider contained in #slider lost.

this website i'm working on. html file: view-source:http://arabiaue.x10.bz/activities/slider%202/demo8.html css file: http://arabiaue.x10.bz/activities/slider%202/js-image-slider.css

there div class.

<div class="sliderinner"><div> 

if inspect slider can find it.

its javascript adding class div , or creating div class together.