p {
    font-size : 18px;
    font-weight: 900;
}

/* 
sélécteur pair et impaire : even & odd
https://www.w3schools.com/cssref/sel_nth-child.asp 
https://www.w3schools.com/cssref/tryit.asp?filename=trycss3_nth-child_odd_even 
*/ 
p:nth-child(odd) {
  color: blue;
}