html, body {
  padding: 25px 0;
  margin: 0;
  font: normal 16px "Helvetica Neue", Arial, sans-serif;
  text-align: center;
  color: #16997c;
  background: url("http://www.psdgraphics.com/wp-content/uploads/2014/02/colorful-triangles.jpg") no-repeat center center fixed; 
  -webkit-background-size: cover;
  -moz-background-size: cover;
  -o-background-size: cover;
  background-size: cover;
}
main {
  display: block;
  max-width: 400px;
  min-width: 250px;
  padding: 20px;
  margin: 0 auto;
  background: rgba(255, 255, 255, 0.5);
  border-radius: 8px;
  box-sizing: border-box;
}
@media (max-width: 480px) {
  main {
    width: 90%;
  }
}
h1 {
  color: #d35400;
}
fieldset {
  padding: 0 0 25px 0;
  margin: 0;
  border: none;
}
input[type="text"] {
  width: 40px;
  height: 40px;
  padding: 10px;
  margin: 0 0 20px 0;
  font: normal 20px "Helvetica Neue", Arial, sans-serif;
  text-align: center;
  border: none;
  box-sizing: border-box;
}
input[type="submit"] {
  display: block;
  width: 50%;
  margin: 0 auto;
  text-align: center;
  padding: 15px 0;
  font: normal 20px Helvetica, Arial, sans-serif;
  color: #ffffff;
  text-shadow: 1px 1px 5px rgba(80, 80, 80, .8);
  border: none;
  background: linear-gradient(to bottom, #f39c12 0%, #d35400 100%);
  -webkit-box-shadow: 0 15px 10px #777;
  -moz-box-shadow: 0 15px 10px #777;
  box-shadow: 0 15px 10px #777;
}
a { 
  color: #d35400; 
  font-size: 1.4em;
  text-decoration: none;
  font-weight: bold;
}
#guess {
  width: 90px;
}