Pseudo class and pseudo elements

 /* PSEUDO CLASS */

/* HOVER */

button:hover {

  background-color: aqua;

  color: black;

}

h3:hover {

  text-transform: uppercase;

}

/* ACTIVE */

button:active {

  color: blue;

  background-color: antiquewhite;

}

p:active {

  font-weight: bold;

  text-decoration: underline;

}

/* CHECKED */

input[type="radio"]:checked + label {

  color: rebeccapurple;

  font-weight: bolder;

}

/* NTH OF TYPE */

p:nth-of-type(2n) {

  background-color: bisque;

}

/* PSEUDO ELEMENTS */

/* FIRST LETTEERS */

p::first-letter {

  font-family: Arial, Helvetica, sans-serif;

}

/* FIRST LINE */

h3::first-line {

  text-decoration: overline;

  background-color: whitesmoke;

}

/* SELECTION */

h1::selection {

  background-color: yellowgreen;

}

/* not a pseudo element or class */

/* !IMPORTANT */

h1 {

  background-color: antiquewhite !important;

}