body {
      font-family: Arial, Helvetica, sans-serif;
      margin: auto;
    }

#header_1 {
    display: block;
    text-align: left;
    color: black;
    background-color: darkseagreen;
    padding: 2.5vh;
    margin: 0%;
    }


.nav_links {
  list-style-type: none;
  margin: 0;
  padding: 0;
  overflow: hidden;
  background-color: #333333;
}

.nav_links li {
  float: left;
}

.nav_links li a {
  display: block;
  color: white;
  text-align: center;
  padding: 14px 16px;
  text-decoration: none;
}

.nav_links li a:hover {
  background-color: #111111;
}