@import url('https://fonts.googleapis.com/css?family=Montserrat&display=swap');

* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
  font-family: 'Montserrat', sans-serif;
}

body {
  display: flex;
  justify-content: center;
  align-items: center;
  min-height: 100vh;
  background: linear-gradient(-45deg, #111, #222, #000, #333);
  background-size: 400% 400%;
  animation: gradientBG 15s ease infinite;
}

@keyframes gradientBG {
  0% {background-position:0% 50%}
  50% {background-position:100% 50%}
  100% {background-position:0% 50%}
}

.container {
  width: 320px;
  padding: 32px 16px;
  border-radius: 18px;
  background: #1c1c1c;
  box-shadow: 5px 5px 15px #0d0d0d, -5px -5px 15px #2c2c2c;
  display: flex;
  flex-direction: column;
  justify-content: space-between;
}

.result {
  width: 100%;
  height: 100px;
  border-radius: 18px;
  background: #111;
  box-shadow: inset 5px 5px 15px #0d0d0d, inset -5px -5px 15px #2c2c2c;
  display: flex;
  align-items: center;
  justify-content: flex-end;
  padding-right: 10px;
}

.result p {
  font-size: 2rem;
  color: #fff;
  overflow-x: auto;
}

.buttons {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  grid-gap: 15px;
  margin-top: 20px;
}

.button, .num-button, .op-button {
  cursor: pointer;
  text-align: center;
  width: 60px;
  height: 60px;
  display: grid;
  place-content: center;
  border-radius: 18px;
  background: #1c1c1c;
  box-shadow: 5px 5px 15px #0d0d0d, -5px -5px 15px #2c2c2c;
  color: #fff;
  font-size: 1.2rem;
  transition: all 0.2s ease;
}

.button:hover, .num-button:hover, .op-button:hover {
  transform: scale(1.1);
  box-shadow: 2px 2px 8px #0d0d0d, -2px -2px 8px #2c2c2c;
  color: #3498db;
}

.zero {
  grid-column: span 2;
}

.calc-action-btn {
  background: #3498db;
  color: #fff;
}

.calc-action-btn:hover {
  background: #1f7dd6;
}