body {
  background-image: url(flag.svg);
  background-position: bottom;
  background-size: 130vh;
  font-family: arial, helvetica, verdana, sans-serif;
  margin: 0;
}

nav {
  background-color: navy;
  display: block;
  font-size: 1.5em;
  font-weight: bolder;
  height: 3em;
  line-height: 1em;
  width: 100%;
}

nav * {
  background-color: navy;
  color: white;
  float: left;
  padding: 1em 0.75em 1em 0.75em;
  text-decoration: none;
}

nav *:hover {
  background-color: lightskyblue;
  color: navy;
  cursor: pointer;
}

#menu,
#toggle {
  display: none;
}

@media screen and (max-width: 520px) {
  #menu {
    display: block;
    float: right;
  }

  nav a {
    box-shadow: 7px 7px 15px -5px grey;
    display: block;
    float: none;
    position: relative;
    width: 150px;
    z-index: 50;
  }

  nav a:not(#main) {
    display: none;
  }

  #main {
    box-shadow: none;
  }
}

#toggle:checked ~ a:not(#main) {
  display: block;
}

header {
  background-image: url(tux.svg);
  background-origin: content-box;
  background-position: left;
  background-repeat: no-repeat;
  background-size: 2em;
  color: darkmagenta;
  font-size: 6vw;
  font-weight: bolder;
  padding: 1.5em 0 2em 1em;
  position: fixed;
  text-indent: 10em;
  z-index: -1;
}

#flipflop {
  background-color: brown;
}