nth-child 3n배수

(3n+1)

(3*0)+1=1;

(3*1)+1=4;

(3*2)+1=7;

(3*3)+1=10;

(3*4)+1=13;

(3*5)+1=16;

 

(3n+2)

(3*0)+2=2;

(3*1)+2=5;

(3*2)+2=8;

(3*3)+2=11;

(3*4)+2=14;

(3*5)+2=17;

 

 

- reference

pjh445 https://pjh445.blog.me/220046988613