submarine.css

html {
  background: url("https://t3.ftcdn.net/jpg/04/02/66/14/240_F_402661479_Nysm7ihwkfDlIChiCX8mgOKhyi6eiWOw.jpg") no-repeat center center fixed;
  background-size: cover;
}

body {
  background-color: lightgreen;
  margin: 0;
  font-family: "Montserrat", "Avenir";
}

h1 {
  text-align: center;
  color: brown;
  font-family: 'Comfortaa', cursive;
  font-size: 3em;
  font-weight: 700;
  padding: 20px 0;
  margin: 0;
  line-height: .66;
  background-color: lightgreen;
}

#instructions {
  font-size: .33em;
  text-align: center;
}

#topNav {
  background-color: lightgreen;
  text-align: center;
  height: 30px;
  color: black;

}

.circle {
  width: 15%;
  background: lightgreen;
  padding-bottom: 15%;
  float: left;
  margin: 2.5%;
  border-radius: 50%;
  transition: background 0.5s;
  -webkit-transition: background 0.5s;
  -moz-transition: background 0.5s;
}

#container {
  max-width: 600px;
  margin: 20px auto;
}

button {
  border: none;
  background: none;
  text-transform: uppercase;
  height: 100%;
  font-weight: 700;
  color: black;
  letter-spacing: 1px;
  font-size: inherit;
  outline: none;
}

button:hover {
  color: white;
  background: steelblue;
}

.selected {
  background: steelblue;
  color: white;
}

#info {
  display: inline-block;
  width: 20%;
  font-weight: 700;
}