styles.css

*,
*::before,
*::after {
  box-sizing: border-box;
}
html,
body {
  min-height: 100%;
  font-family: 'Open Sans', sans-serif;
}
body {
  background: linear-gradient(50deg, #f3c680, hsla(179, 54%, 76%, 1));
}

/*--------------------
Buttons
--------------------*/
.btn {
  display: block;
  background: hsl(86, 76%, 71%);
  color: hsl(0, 0, 100);
  text-decoration: none;
  margin: 20px 0;
  padding: 15px 15px;
  border-radius: 5px;
  position: relative;
}

.btn::after {
  content: '';
  position: absolute; /* Added 'absolute' position */
  z-index: 1;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  transition: all 0.2s ease-in-out;
  box-shadow: inset 0 3px 0 hsla(0, 0, 0, 0), 0 3px 3px hsla(0, 0, 0, 0.2);
  border-radius: 5px;
}

.btn:hover::after {
  background: hsla(0, 0, 0, 0.1);
  box-shadow: inset 0 3px 0 hsla(0, 0, 0, 0.2);
}

/*--------------------
Form
--------------------*/
.form {
  fieldset {
    border: none;
    padding: 0;
    padding: 10px 0;
    position: relative;
    clear: both;
  }

  .fieldset-expiration {
    float: left;
    width: 60%;

    .select {
      width: 84px;
      margin-right: 12px;
      float: left;
    }
  }

  .fieldset-ccv {
    clear: none;
    float: right;
    width: 86px;
  }

  label {
    display: block;
    text-transform: uppercase;
    font-size: 11px;
    color: hsla(0, 0, 0, 0.6);
    margin-bottom: 5px;
    font-weight: bold;
    font-family: Inconsolata;
  }

  input,
  .select {
    width: 100%;
    height: 38px;
    color: hsl(0, 0, 20);
    padding: 10px;
    border-radius: 5px;
    font-size: 15px;
    outline: none !important;
    border: 1px solid hsla(0, 0, 0, 0.3);
    box-shadow: inset 0 1px 4px hsla(0, 0, 0, 0.2);
  }

  .input-cart-number {
    width: 82px;
    display: inline-block;
    margin-right: 8px;
  }

  .input-cart-number:last-child {
    margin-right: 0;
  }

  .select {
    position: relative;
  }

  .select::after {
    content: '';
    border-top: 8px solid #222;
    border-left: 4px solid transparent;
    border-right: 4px solid transparent;
    position: absolute;
    z-index: 2;
    top: 14px;
    right: 10px;
    pointer-events: none;
  }

  select {
    appearance: none;
    position: absolute;
    padding: 0;
    border: none;
    width: 100%;
    outline: none !important;
    top: 6px;
    left: 6px;
    background: none;
  }

  button {
    width: 100%;
    outline: none !important;
    background: linear-gradient(180deg, #49a09b, #3d8291);
    text-transform: uppercase;
    font-weight: bold;
    border: none;
    box-shadow: none;
    text-shadow: 0 1px 2px rgba(0, 0, 0, 0.2);
    margin-top: 90px;
  }

  button .fa {
    margin-right: 6px;
  }
}

/*--------------------
Checkout
--------------------*/
.checkout {
  margin: 150px auto 30px;
  position: relative;
  width: 460px;
  background: white;
  border-radius: 15px;
  padding: 160px 45px 30px;
  box-shadow: 0 10px 40px hsla(0, 0, 0, 0.1);
}

/*--------------------
Credit Card
--------------------*/
.credit-card-box {
  perspective: 1000;
  width: 400px;
  height: 280px;
  position: absolute;
  top: -112px;
  left: 50%;
  transform: translateX(-50%);
}

.credit-card-box:hover .flip,
.credit-card-box.hover .flip {
  transform: rotateY(180deg);
}

.front,
.back {
  width: 400px;
  height: 250px;
  border-radius: 15px;
  backface-visibility: hidden;
  background: linear-gradient(135deg, #bd6772, #53223f);
  position: absolute;
  color: #fff;
  font-family: Inconsolata;
  top: 0;
  left: 0;
  text-shadow: 0 1px 1px hsla(0, 0, 0, 0.3);
  box-shadow: 0 1px 6px hsla(0, 0, 0, 0.3);
}

.front {
  z-index: 2;
  transform: rotateY(0deg);
}

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

.flip {
  transition: 0.6s;
  transform-style: preserve-3d;
  position: relative;
}

.logo {
  position: absolute;
  top: 9px;
  right: 20px;
  width: 60px;
}

.front .logo {
  top: 9px;
  right: 20px;
}

.back .logo {
  top: 185px;
}

.chip {
  position: absolute;
  width: 60px;
  height: 45px;
  top: 20px;
  left: 20px;
  background: linear-gradient(135deg, hsl(269, 54%, 87%) 0%, hsl(200, 64%, 89%) 44%, hsl(18, 55%, 94%) 100%);
  border-radius: 8px;
}

.chip::before {
  content: '';
  position: absolute;
  top: 0;
  bottom: 0;
  left: 0;
  right: 0;
  margin: auto;
  border: 4px solid hsla(0, 0, 50, 0.1);
  width: 80%;
  height: 70%;
  border-radius: 5px;
}

.strip {
  background: linear-gradient(135deg, hsl(0, 0, 25%), hsl(0, 0, 10%));
  position: absolute;
  width: 100%;
  height: 50px;
  top: 30px;
  left: 0;
}

.number {
  position: absolute;
  margin: 0 auto;
  top: 103px;
  left: 19px;
  font-size: 38px;
}

.card-holder,
.card-expiration-date {
  position: absolute;
  margin: 0 auto;
  top: 180px;
  left: 19px;
  font-size: 22px;
  text-transform: capitalize;
}

.card-expiration-date {
  text-align: right;
  left: auto;
  right: 20px;
}

.ccv {
  height: 36px;
  background: #fff;
  width: 91%;
  border-radius: 5px;
  top: 110px;
  left: 0;
  right: 0;
  position: absolute;
  margin: 0 auto;
  color: #000;
  text-align: right;
  padding: 10px;
}

.ccv label {
  margin: -25px 0 14px;
  color: #fff;
}

.the-most {
  position: fixed;
  z-index: 1;
  bottom: 0;
  left: 0;
  width: 50vw;
  max-width: 200px;
  padding: 10px;
}

.the-most img {
  max-width: 100%;
}