h1 {
 text-align: center;
}
body {
  background-color: black;
}
div {
  padding: 50px;
  background: black;
  margin: 0;
border-radius: 10px;
}

p {
color: gray;
}

ul {
  list-style-type: none;
  margin: 0;
  padding: 0;
  background-color: #333333;
display: flex;
  justify-content: center;
 outline: thick solid green;
  border-radius: 10px;
}

ul li {
  float: left;
}

li a {
  display: block;
  color: #43E831;
  padding: 8px 16px;
  text-decoration: none;
}

li a.active {
  background-color: #04AA6D;
  color: white;
}

li a:hover:not(.active) {
  background-color: #43E831;
  color: white;
}