body {
  height: 100vh;
  overflow: hidden;
  background-color: cadetblue;
  display: flex;
  justify-content: space-evenly;
  align-items: center;
  flex-direction: column;
}
.header{
    font-size: 7vh;
    font-weight: 900;
    color: antiquewhite;
    height: 5vh;
}
.card {
  height: 15vh;
  width: 7vw;
  border: 2px solid black;
  box-sizing: border-box;
  transform-style: preserve-3d;
  transition: transform 0.6s ease;
  cursor: pointer;
  position: relative;
}

.front,
.back {
  height: 100%;
  width: 100%;
  position: absolute;
  top: 0;
  left: 0;
  backface-visibility: hidden;
}

.front {
  background-color: aqua;
}

.back {
  transform: rotateY(180deg);
}

.all-cards {
  display: grid;
  grid-template-columns: repeat(4, 7vw);
  gap: 1vh;
}

.btn {
  right: 10vw;
  padding: 2vh;
  font-size: 3vh;
  border-radius: 2vh;
  background-color: cornsilk;
  font-weight: bolder;
  cursor: pointer;
  font-family: "Gill Sans", "Gill Sans MT", Calibri, "Trebuchet MS", sans-serif;
  transition: all 0.5s ease;
}
.btn:hover {
  background-color: burlywood;
}
.footer {
  bottom: 2vh;
  right: 10vw;
  font-size: 3vh;
  font-weight: bold;
  color: white;
  font-family: cursive;
}

@media (max-width: 600px) {
  body {
    display: flex;
    flex-direction: column;
    justify-content: flex-start;
  }
  .card {
    height: 10vh;
    width: 20vw;
  }
  .all-cards {
    margin-bottom: 10vh;
    margin-top: 10vh;
    display: grid;
    grid-template-columns: repeat(4, 20vw);
    gap: 1vh;
  }
  .btn {
    position: static;
    font-family: fantasy;
  }
  .footer {
    bottom: 2vh;
    position: fixed;
  }
  .header{
    margin-top: 2vh;
    font-size: 4vh;
  }
}