*{
  margin: 0;
  padding: 0;
}
body{
  font-family:"Arial";
  font-size: 20pt;
}
h1{
  width: 100%;
  height: auto;
  text-align: center;
}
nav{
  display: inline-block;
  position: relative;
  width: 100%;
  height: auto;
}
nav a{
  display: inline-block;
  text-decoration: none;
  color: black;
  cursor: pointer;
  line-height: 1;
  text-align: center;
}
nav a:after{
  display: block;
  left: 0;
  width: 0;
  height: 3px;
  background-color: black;
  content: "";
  transition: width 0.3s ease-out;
}
nav a:hover:after,
nav a:focus:after {
  width: 100%;
}
nav ul{
  list-style: none;
  padding: 0;
  margin: 0 auto;
  width: 900px;
  height: auto;
}
nav li{
  text-align: center;
  display: inline-block;
  padding: 0 0 20px 20px;
}
.sub-menu {
  transition: 0.3s ease;
  display: none;
}
.sub-menu:hover li{
  display: block;
}

/*Если экран меньше 800px то выполняются эти стили*/
@media screen and (max-width: 800px) {
  nav{
    border-bottom: 0;
  }
  nav ul{
    position: relative;
    display: block;
    height: auto;
    left: 0;
  }
  nav a#pull{
    display: block;
    width: 100%;
    position: relative;
  }
  nav a#pull:after{
    content: "";
    width: 30px;
    height: 30px;
    display: inline-block;
    position: absolute;

  }
  nav li{
    height: auto;
    text-align: left;
    display: block;
  }
}