body {
  text-align: center;
  background-color: #011F3F;
  margin: 0;
  padding: 0;
  font-family: Arial, sans-serif;
}

#level-title {
  font-size: 2rem;
  margin: 5%;
  color: #FEF2BF;
}

#start-btn {
  display: inline-block;
  margin-bottom: 20px;
  padding: 10px 20px;
  font-size: 1.2rem;
  background-color: #FEF2BF;
  border: 2px solid #000;
  border-radius: 5px;
  cursor: pointer;
}

.container {
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  align-items: center;
  width: 100%;
  max-width: 600px;
  margin: auto;
}

.row {
  width: 100%;
  display: flex;
  justify-content: center;
}

.btn {
  margin: 10px;
  display: inline-block;
  height: 100px;
  width: 100px;
  border: 10px solid black;
  border-radius: 20%;
  box-sizing: border-box;
}

.game-over {
  background-color: red;
  opacity: 0.8;
}

.red {
  background-color: red;
}

.green {
  background-color: green;
}

.blue {
  background-color: blue;
}

.yellow {
  background-color: yellow;
}

.pressed {
  box-shadow: 0 0 20px white;
  background-color: grey;
}

@media (min-width: 600px) {
  .btn {
    height: 150px;
    width: 150px;
  }

  #level-title {
    font-size: 2.5rem;
  }
}