styles.css

* {
  margin: 0;
  box-sizing: border-box;
}
div {
  background-color: #ff000022;
  width: 100%;

  height: 50px;
  /* Aplicar margin em todos os lados igualmente */
  /* margin: 10px; */

  /* Aplicar margin no vertical e horizontal */
  /* margin: 100px 200px; */

  /* Aplicar margin no top, right, bottom, left */
  /* margin: 10px 20px 30px 40px; */

  /* Aplicar margin no top, horizontal e bottom */
  /* margin: 10px 30px 40px; */

  /* margin: 0 0 0 10px; */

  /* margin-left: 10px;
  margin-right: 10px;
  margin-top: 10px;
  margin-bottom: 10px; */

  padding: 10px;
  /* padding: 10px 20px; */
  /* padding: 10px 20px 30px 40px; */
  /* padding: 10px 30px 40px; */
  /* padding: 0 0 0 10px; */
  /* padding-left: 10px;
  padding-right: 10px;
  padding-top: 10px;
  padding-bottom: 10px; */

  border: 2px solid blue;
  /* border-style: solid;
  border-width: 10px;
  border-color: red; */
  border-radius: 5px;
  font-size: 30px;
}
html {
  font-size: 12px;
}
h1 {
  /* font-size: 1em; */
  font-size: 1rem;
  /*
  em
  rem
  %
  vh
  vw 
  */
}
main {
  background-color: green;
  height: 100vh;
  width: 100vw;
}