The difference between spaces and no spaces between two classes in css

There is a space, which means: descendant iteration selector,

No spaces, means: also contains class

for example:

.swiperA .swiperB .swiper{

background-color:red;

}   

.swiperA .swiperB.swiper{

background-color:blue;

} 

The background color of area A will be red

The background color of area B is blue