style.css

/* Font */
@import url("https://fonts.googleapis.com/css2?family=Lato&display=swap");

/* Basic Styles */
:root {
  --dark: #243441;
  --orange: #ec802e;
}
* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
  font-family: "Lato", sans-serif;
}
body {
  background-color: #ffc397;
}
body .container {
  height: 93vh;
}
.text-custom {
  color: var(--orange);
}
#calculator {
  background-color: var(--dark);
  width: 250px;
  margin: 0 auto;
  padding: 15px 10px 20px 10px;
  border-radius: 20px;
  box-shadow: 4px 4px 12px 5px rgb(31, 31, 31);
}
#calculator #display {
  height: 150px;
  background-color: #17242e;
  border-radius: 20px 20px 5px 5px;
  margin-bottom: 10px;
  padding: 20px 5px;
  box-shadow: inset -1px -1px 5px 1px rgb(90, 90, 90);
  overflow: hidden;
}
#result {
  display: block;
  font-size: 45px;
  color: white;
  text-align: right;
  overflow: hidden;
}
#preview {
  display: block;
  color: gray;
  text-align: right;
}
#buttons {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 10px;
}
#buttons button {
  color: white;
  padding: 10px 15px;
  border: none;
  border-radius: 10px;
  background-color: #17242e;
  box-shadow: inset 0 2px 3px 0px rgb(91, 93, 105), 0px 2px 6px 0px black;
}
#buttons button[class="sign"],
#buttons button[class="control"] {
  color: var(--orange);
}
#buttons button[id="equal"] {
  background-color: var(--orange);
  color: white;
  grid-column: 3 / span 2;
}
#buttons button:active {
  transform: translate(1.5px, 1.5px);
  box-shadow: inset 0 2px 0px 0px rgb(32, 32, 32), 0px 2px 0px 0px rgb(46, 46, 46);
}
#buttons button:focus {
  outline: none;
}
.footer {
  text-align: center;
}
.copyright {
  color: var(--dark);
}
.footer a {
  text-decoration: none;
  color: rgb(180, 100, 0);
}

/* Responsive Extra */
@media only screen and (max-width:768px) {
  body .container {
    margin: 20px 0;
    height: auto;
  }
}