.container {
  width: 90%;
  max-width: 1300px;
  margin: 10px auto;
  top: 0;
}
#header {
  display: flex;
  margin: auto;
  width: 90%;
  padding: 0;
}
#header img {
  width: 100%;
}

body {
  background-image: url("back.png");
  background-repeat: no-repeat;
  background-position: center top;
  background-size: cover;
}

ul {
  list-style-type: none;
  padding: 0;
  overflow: hidden;
  background-color: black;
  opacity: 0.8;
  display: flex;
  justify-content: center;
  padding-top: 0;
}
ul li {
  float: left;
}
ul li a {
  padding: 90px;
  width: 200px;
  font-size: 25px;
  text-decoration: none;
  color: white;
  font-family: Arial, Helvetica, sans-serif;
}

.flex-container {
  display: flex;
  flex-direction: row;
  justify-content: center;
}
.flex-container div {
  display: flex;
  margin: 15px;
}
a:link {
  color: white;
  text-decoration: none;
}
a:visited {
  color: white;
  background-color: black;
}
a:hover {
  text-decoration: none;
  color: red;
  background-color: black;
}

a:active {
  color: firebrick;
  background-color: black;
}
footer {
  position: relative;
  bottom: 0;
  left: 0;
  width: 90;
  color: white;
  background-color: black;
  padding: 8px;
  text-align: center;
  z-index: 1000;
  margin: auto;
  width: 90%;
}