hr {

margin: 10px;

}

h1 {

text-align: center;

}

.nav-ul {

list-style-type: none;

}

.nav-li {

padding: 10px;
margin: 10px;
display: inline;

}

.content {

margin: 30px;

}

@media only screen and (max-width: 800px) {

/* For tablets: */
.content {
  margin: 20px;
}

}

@media only screen and (max-width: 500px) {

/* For mobile phones: */
.content {
  margin: 10px;
}

}