* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
  font-family: consolas;
}

body {
  display: flex;
  justify-content: center;
  align-items: center;
  min-height: 100vh;
  background: #333;
}
body.light {
  background: #f8f8f8;
}
.container {
  position: relative;
  min-width: 300px;
  min-height: 400px;
  background: #333;
  padding: 40px 30px 30px;
  border-radius: 20px;
  box-shadow: 25px 25px 75px rgba(0, 0, 0, 0.25),
    10px 10px 70px rgba(0, 0, 0, 0.25), inset -5px -5px 15px rgba(0, 0, 0, 0.5),
    inset 5px 5px 15px rgba(0, 0, 0, 0.5);
}
body.light .container {
  background: #fafafa;
  box-shadow: 25px 25px 75px rgba(0, 0, 0, 0.15),
    10px 10px 70px rgba(0, 0, 0, 0.15), inset -5px -5px 15px rgba(0, 0, 0, 0.15),
    inset 5px 5px 15px rgba(0, 0, 0, 0.05);
}
.calculator {
  position: relative;
  display: grid;
}
.calculator .value {
  position: relative;
  grid-column: span 4;
  height: 100px;
  left: 10px;
  width: calc(100% - 20px);
  border: none;
  outline: none;
  background: #a7af7c;
  margin-bottom: 10px;
  border-radius: 10px;
  box-shadow: 0 0 0 2px rgba(0, 0, 0, 0.75);
  text-align: right;
  padding: 10px;
  font-size: 2em;
}

.calculator span {
  position: relative;
  display: grid;
  place-items: center;
  width: 80px;
  height: 80px;
  margin: 8px;
  background: linear-gradient(180deg, #2f2f2f, #3f3f3f);
  box-shadow: inset -8px 0 8px rgba(0, 0, 0, 0.15),
    inset 0 -8px 8px rgba(0, 0, 0, 0.25), 0 0 0 2px rgba(0, 0, 0, 0.75),
    10px 20px 25px rgba(0, 0, 0, 0.4);
  color: #fff;
  user-select: none;
  cursor: pointer;
  font-weight: 400;
  border-radius: 10px;
}
body.light .calculator span {
  background: linear-gradient(180deg, #fafafa, #f4f4f4);
  box-shadow: inset -8px 0 8px rgba(0, 0, 0, 0.15),
    inset 0 -8px 8px rgba(0, 0, 0, 0.15), 0 0 0 2px rgba(0, 0, 0, 1),
    10px 20px 25px rgba(0, 0, 0, 0.25);
}
.calculator span::before {
  content: "";
  position: absolute;
  top: 3px;
  left: 4px;
  bottom: 14px;
  right: 12px;
  background: linear-gradient(90deg, #2d2d2d, #4d4d4d);
  border-radius: 10px;
  box-shadow: -5px -5px 15px rgba(0, 0, 0, 0.15),
    10px 5px 10px rgba(0, 0, 0, 0.15);
  border-left: 1px solid #0004;
  border-bottom: 1px solid #0004;
  border-top: 1px solid #0009;
}
body.light .calculator span::before {
  background: linear-gradient(90deg, #e6e6e6, #efefef);
  border-radius: 10px;
  box-shadow: -10px -10px 10px rgba(225, 225, 225, 0.25),
    10px 5px 10px rgba(0, 0, 0, 0.15);
  border-left: 1px solid #fff4;
  border-bottom: 1px solid #fff4;
  border-top: 1px solid #fff9;
}
.calculator span:active {
  filter: brightness(1.5);
}
body.light .calculator span:active {
  filter: brightness(0.9);
}
.calculator span i {
  position: relative;
  font-style: normal;
  font-size: 1.5em;
  text-transform: uppercase;
}
body.light .calculator span i {
  color: #333;
}
body.light .calculator span.clear i,
body.light .calculator span.equal i {
  color: #fff;
}
body.light .calculator .clear,
.calculator .clear {
  grid-column: span 2;
  width: 180px;
  background: #f00;
}
body.light .calculator .clear::before,
.calculator .clear::before {
  background: linear-gradient(90deg, #d20000, #ffffff5c);
  border-left: 1px solid #fff4;
  border-bottom: 1px solid #fff4;
  border-top: 1px solid #fff4;
}
.calculator .plus {
  grid-row: span 2;
  height: 180px;
}
body.light .calculator .equal,
.calculator .equal {
  background: #2196f3;
}
body.light .calculator .equal::before,
.calculator .equal::before {
  background: linear-gradient(90deg, #1479c9, #ffffff5c);
  border-left: 1px solid #fff4;
  border-bottom: 1px solid #fff4;
  border-top: 1px solid #fff4;
}

.btn {
  position: absolute;
  top: 20px;
  right: 20px;
  width: 60px;
  height: 60px;
  background: #333;
  font-size: 1.5em;
  box-shadow: 5px 5px 15px rgba(0, 0, 0, 0.25), 5px 5px 30px rgba(0, 0, 0, 0.25),
    inset -2px -2px 5px rgba(0, 0, 0, 0.25),
    inset 2px 2px 5px rgba(0, 0, 0, 0.25);
  display: flex;
  justify-content: center;
  align-items: center;
  cursor: pointer;
  border-radius: 10px;
}
body.light .btn {
  background: #fafafa;
  box-shadow: 5px 5px 15px rgba(0, 0, 0, 0.1), 5px 5px 30px rgba(0, 0, 0, 0.05),
    inset -2px -2px 5px rgba(0, 0, 0, 0.1),
    inset 2px 2px 5px rgba(0, 0, 0, 0.05);
}
.btn strong {
  display: none;
}
.btn strong:nth-child(1) {
  display: block;
}
body.light .btn strong:nth-child(1) {
  display: none;
}
body.light .btn strong:nth-child(2) {
  display: block;
}