CSS Styling Table

Question

I tried to coloring it with the pseudo selector, but it went weird. What's wrong with this code?
https://sololearn.com/compiler-playground/WtMo765cTZkk/?ref=app

Answer 1

tr:nth-child(1) is th

also, why not just use odd-even?

tr:nth-child(odd){
background-color:blue;
}

tr:nth-child(even){
background-color:red;
}

Answer 2

Bob_Li Thank you, I thought the header was a separate code, so it didn't count in the pseudo selector.