Class selectors are given an overall block, whereas id selectors simply accept a single element that differs from other components.

Class Selector in CSS

<style>    
.center {    
    text-align: center;    
    color: blue;    
}    
</style>

CSS Id Selector

<style>    
#para1 {    
    text-align: center;    
    color: blue;    
}    
</style>