style.css

* {
  margin: 0px;
  padding: 0px;
  box-sizing: border-box;
}
body {
  background-color: #d2d3de;
}

/* calculator */
#cal {
  margin-top: 10vh;
  width: fit-content;
  margin-left: auto;
  margin-right: auto;
  background-color: #d2d3de;

  box-shadow: 12px 12px 16px 0 rgba(0, 0, 0, 0.2),
    -8px -8px 12px 0 rgba(255, 255, 255, 0.3);
  border-radius: 25px;
}

/* display */

#display {
  margin-top: 20px;
  height: 10vh;
  text-align: right;
  color: rgba(0, 0, 0, 0.4);
  font-size: larger;
  font-weight: bold;
  padding: 30px;
}

/* input */
#input input {
  width: 100%;
  text-align: right;
  font-size: large;
  color: rgba(0, 0, 0, 0.4);
  background-color: #d2d3de;
  border: none;
  padding: 25px;
  font-weight: bold;
  box-shadow: 12px 12px 16px 0 rgba(255, 255, 255, 0.3) inset,
    -8px -8px 12px 0 rgba(0, 0, 0, 0.25) inset;
  border-radius: 25px;
}

/* buttons */
#key {
  display: flex;
  justify-content: center;
  align-items: center;
  background-color: #d2d3de;
  border-radius: 25px;
}

#key table {
  border: 4px solid #d2d3de;
  border-radius: 25px;
  box-shadow: 12px 12px 16px 0 rgba(255, 255, 255, 0.2) inset,
    -8px -8px 12px 0 rgba(0, 0, 0, 0.25) inset;
}
#key table td input {
  width: 70px;
  height: 75px;
  color: rgba(0, 0, 0, 0.4);
  font-size: x-large;
  background-color: #d2d3de;
  padding: 20px;
  outline: none;
  text-align: center;
  cursor: pointer;
  border: none;
  box-shadow: 12px 12px 16px 0 rgba(0, 0, 0, 0.2),
    -8px -8px 12px 0 rgba(255, 255, 255, 0);
  -webkit-user-select: none;
  -khtml-user-select: none;
  -moz-user-select: none;
  -ms-user-select: none;
  -o-user-select: none;
  user-select: none;
}
#key table td input:active {
  box-shadow: 12px 12px 16px 0 rgba(255, 255, 255, 0.3) inset,
    -8px -8px 12px 0 rgba(0, 0, 0, 0.25) inset;
}