@import url("https://fonts.googleapis.com/css2?family=Poppins:wght@200;400;500&display=swap");
* {
  padding: 0;
  margin: 0;
  outline: 0;
}
header {
  display: flex;
  justify-content: center;
  align-items: center;
  font-family: "Poppins", sans-serif;
  color: #ecf0f1;
  font-size: 1.5rem;
  padding: 1em;
}
main {
  display: grid;
  place-items: center;
  min-height: 100%;
}
body {
  background-image: url(../images/mesh-527.png);
  background-size: cover;
}
.container {
  display: grid;
  grid-template: repeat(4, 1fr) / repeat(4, 1fr);
  justify-content: center;
  align-items: center;
  gap: 10px;
}
.card {
  height: 120px;
  width: 120px;
  position: relative;
  transform-style: preserve-3d;
  transition: transform 0.5s;
}
.face > img {
  width: 100px;
  height: 100px;
}
.face {
  position: absolute;
  pointer-events: none;
  width: 100%;
  height: 100%;
  border-radius: 5px;
  transform: scale(1);
  display: flex;
  align-items: center;
  justify-content: center;
  background-color: #2c3e50;
  backface-visibility: hidden;
}

.back-face {
  background-color: #3498db;
  transform: rotateY(180deg);
}

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

#btn {
  display: inline-block;
  outline: 0;
  border: 0;
  cursor: pointer;
  transition: box-shadow 0.15s ease, transform 0.15s ease;
  will-change: box-shadow, transform;
  background: #fcfcfd;
  box-shadow: 0px 2px 4px rgb(45 35 66 / 40%),
    0px 7px 13px -3px rgb(45 35 66 / 30%), inset 0px -3px 0px #d6d6e7;
  height: 48px;
  padding: 0 32px;
  font-size: 18px;
  border-radius: 6px;
  color: #36395a;
  transition: box-shadow 0.15s ease, transform 0.15s ease;
}
#btn:hover {
  box-shadow: 0px 4px 8px rgb(45 35 66 / 40%),
    0px 7px 13px -3px rgb(45 35 66 / 30%), inset 0px -3px 0px #d6d6e7;
  transform: translateY(-2px);
}
#btn:active {
  box-shadow: inset 0px 3px 7px #d6d6e7;
  transform: translateY(2px);
}

.btn-div {
  margin-top: 1em;
  visibility: hidden;
}