styles.css

body {
  text-align: center;
  background-color: #0e0220;
}

#level-title {
  font-family: 'Righteous', cursive;
  font-size: 3rem;
  margin: 5%;
  color: #48e0e4;
}

.container {
  display: flex;
  width: 50%;
  margin: auto;
  flex-direction: row;
  justify-content: center;
  align-items: center;
  justify-content: space-evenly;
}

.btn {
  margin: 25px;
  display: inline-block;
  height: 120px;
  width: 120px;
  border: 10px solid #1b1b2f;
  border-radius: 20%;
  cursor: pointer;
  outline: none;
}

.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: 2px 2px 15px #d7fbf6;
  background-color: grey;
}

.again {
  padding: 1rem;
  color: #d7fbf6;
  font-family: 'Prompt', sans-serif;
}

button {
  border: none;
  cursor: pointer;
  font-size: 1.2rem;
  font-family: 'Prompt', sans-serif;
  outline: none;
  background: #c6f50c;
  background-image: -webkit-linear-gradient(top, #c6f50c, #a0ab0d);
  background-image: -moz-linear-gradient(top, #c6f50c, #a0ab0d);
  background-image: -ms-linear-gradient(top, #c6f50c, #a0ab0d);
  background-image: -o-linear-gradient(top, #c6f50c, #a0ab0d);
  background-image: linear-gradient(to bottom, #c6f50c, #a0ab0d);
  -webkit-border-radius: 28;
  -moz-border-radius: 28;
  border-radius: 28px;
  color: #ffffff;
  padding: 6px 20px 6px 20px;
  text-decoration: none;
}

button:hover,
button:focus {
  background: #b4db18;
  background-image: -webkit-linear-gradient(top, #b4db18, #c0d934);
  background-image: -moz-linear-gradient(top, #b4db18, #c0d934);
  background-image: -ms-linear-gradient(top, #b4db18, #c0d934);
  background-image: -o-linear-gradient(top, #b4db18, #c0d934);
  background-image: linear-gradient(to bottom, #b4db18, #c0d934);
  text-decoration: none;
}

#highestLevel {
  padding: 1rem;
  color: #d7fbf6;
  font-family: 'Prompt', sans-serif;
  display: none;
}

/* Instructions */
#instruction {
  position: fixed;
  right: 1rem;
  bottom: 0.5rem;
  color: white;
  border-radius: 100%;
}

#instruction:hover,
#instruction:focus {
  cursor: pointer;
  box-shadow: 0.8px 0.8px 5px white;
}

/* card */
#card {
  position: fixed;
  width: 60%;
  margin: 0 auto;
  left: 0;
  right: 0;
  height: 50%;
  background-color: white;
  font-family: 'Prompt', sans-serif;
  z-index: 1;
  border-radius: 10px;
  visibility: hidden;
  transition: 0.2s ease-in-out;
}

#close {
  font-size: 3rem;
  position: absolute;
  cursor: pointer;
  line-height: 0.5;
  right: 0.8rem;
  top: 0.4rem;
}

#card h3 {
  border-bottom: 1.5px solid #0e0220;
}

#card ul {
  text-align: left;
}

@media screen and (max-width:600px) {
  .container {
    width: 90%;
  }

  .btn {
    width: 100px;
    height: 100px;
  }

  #level-title {
    font-size: 2.2rem;
  }

  #card {
    width: 90%;
    height: 60%;
  }
}