style.css

*{
    padding: 0;
    margin: 0;
    box-sizing: border-box;
    font-family: 'Space Grotesk', sans-serif;
}
.popup{
  width: 750px;
  padding: 30px 40px;
  margin-left: 23%;
  margin-top: 6.5%;
  position: absolute;
  background: rgba(255, 255, 255, 0.178);
  box-shadow: 0 8px 32px 0 rgba( 31, 38, 135, 0.37 );
  backdrop-filter: blur( 4px );
  -webkit-backdrop-filter: blur( 4px );
  border-radius: 20px;
  display: none;
  animation: slideTop 1s ease forwards;
  opacity: 0;
}
@keyframes slideTop{
  0%{
      transform: translateY(-100rem);
      opacity: 0;
  }
  100%{
      transform: translateY(0rem);
      opacity: 1;
  }
}
.welcome{
  color: #ffffff;
}
.close{
  padding: 1%;
  margin-top: 5%;
  width: 110px;
  border-radius: 20px;
  border: none;
  background-color: aqua;
  font-size: 15px;
  font-weight: 600;
  cursor: pointer;
}
.close:hover{
  box-shadow: 2px 4px 32px 2px aqua;
  transform: scale(1.1);
  transition: 0.5s;
}
.wrapper{
  display: none;
}

body {
    text-align: center;
    background-image: url(back_grad.png);
    background-size: auto;
    background-repeat: no-repeat;
    overflow: hidden;
    justify-content: center;
}

#level-title {
    font-size: 3rem;
    margin:  3%;
    color: transparent;
    animation: effect 2s linear infinite;
  }


@keyframes effect {
        0% {
            background: linear-gradient(
                #ff3c00, #ffd902);
            -webkit-background-clip: text;
        }
        
        100% {
            background: linear-gradient(
                #48ff24, #1d64ff);
            -webkit-background-clip: text;
        }
}

.container 
{
    width: 50%;
    margin: auto;
    animation: zoomin 1.2s ease forwards;
    animation-delay: 0.5s;
    opacity: 0;
}
@keyframes zoomin{
  0%{
      transform: scale(0);
      opacity: 0;
  }
  100%{
      transform: scale(1);
      opacity: 1;
  }
}
.btn{
  display: inline-block;
  width: 170px;
  height: 170px;
  border-radius: 20%;
  border: none;
  margin: 1.5%;
  cursor: pointer;
}

.red {
  background-color: rgb(255, 0, 0);
}

.green {
  background-color: rgb(4, 255, 4);
}

.blue {
  background-color: rgb(24, 86, 255);
}

.yellow {
  background-color: rgb(229, 255, 0);
}

.game-over {
  background-color: #c50000;
  opacity: 0.8;
  background-image: none;
}

#stBtn{
  margin: 4%;
  width: 120px;
  padding: 1%;
  border-radius: 20px;
  border: none;
  background-image: linear-gradient(90deg, #ff3c00, #ffd902,#48ff24, #1d64ff);
  font-size: 16px;
  font-weight: 600;
  color: rgb(29, 27, 27);
  cursor: pointer;
  animation: zoomin 1.5s ease forwards;
  animation-delay: 1s;
  opacity: 0;
}
@keyframes zoomin{
  0%{
      transform: scale(0);
      opacity: 0;
  }
  100%{
      transform: scale(1);
      opacity: 1;
  }
}
.pressed {
  box-shadow: 0 0 20px white;
  background-color: grey;
}


@media screen and (max-width: 600px){
.popup{
 width: auto;
 font-size: 12px;
 left: 10%; right:10%; top: 10%; bottom: 10%;
 margin: auto;
 position: absolute;
}
.wrapper{
  margin-top: 15%;
}
#level-title {
  font-size: 1.5rem;
  margin: 5%;
}
.container{
  margin-top: 10%;
}
.btn{
  width: 130px;
  height: 130px;
}
#stBtn{
  margin-top: 15%;
}
}

@media screen and (max-width: 400px){
  .popup{
   width: auto;
   font-size: 12px;
   left: 6%; right:6%; top: 10%; bottom: 10%;
   margin: auto;
   position: absolute;
  }
  .wrapper{
    margin-top: 12%;
  }
  #level-title {
    font-size: 1.5rem;
    margin: 5%;
  }
  .container{
    margin-top: 7%;
  }
  .btn{
    width: 92px;
    height: 92px;
  }
  #stBtn{
    margin-top: 12%;
  }
  }