Regarding the proper CSS Syntax

Hi dev,
       Can we use the below block1 in a CSS.Is it correct in syntax wise?
   block1

    para:first-child {
        text-indent: 0;
    }
 
or should this be the block2,
block2
    p:first-child {

        text-indent: 0;
    }
??

Or else is there any proper way that we can use the block1 in our CSS directly?