@import url("https://fonts.googleapis.com/css2?family=Quicksand:wght@300;400;500&display=swap");

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

body {
  display: flex;
  justify-content: center;
  align-items: center;
  min-height: 100vh;
  background: #091921;
  position: relative;
  overflow: hidden;
}

body::before, body::after {
  content: "";
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  z-index: 0;
}

body::before {
  background: linear-gradient(#e91e63, #ffc107);
  clip-path: circle(22% at 30% 20%);
}

body::after {
  background: linear-gradient(#ffffff, #da00ff);
  clip-path: circle(20% at 70% 90%);
}

.container {
  position: relative;
  background: rgba(255, 255, 255, 0.05);
  border-radius: 8px;
  overflow: hidden;
  z-index: 10;
  border-top: 1px solid rgba(255, 255, 255, 0.2);
  border-left: 1px solid rgba(255, 255, 255, 0.2);
  box-shadow: 5px 5px 30px rgba(0, 0, 0, 0.2);
  width: 95vw;    /* almost full width on small devices */
  max-width: 400px; /* limit max width on large devices */
  margin: 0 auto;
  padding: 0.5rem 0.5rem;
}

.calculator {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  grid-auto-rows: 80px;
  gap: 0;
}

.value {
  grid-column: span 4;
  height: 140px;
  width: 100%;
  text-align: right;
  border: none;
  outline: none;
  padding: 15px;
  font-size: 2.5rem;
  background: transparent;
  color: #fff;
  border-bottom: 1px solid rgba(255, 255, 255, 0.05);
  border-right: 1px solid rgba(255, 255, 255, 0.05);
  resize: none;
  line-height: 1.2;
}

.calculator span {
  display: grid;
  place-items: center;
  width: 100%;
  height: 100%;
  color: #fff;
  font-weight: 400;
  cursor: pointer;
  font-size: 1.5rem;
  user-select: none;
  border-bottom: 1px solid rgba(255, 255, 255, 0.05);
  border-right: 1px solid rgba(255, 255, 255, 0.05);
}

span.clear {
  grid-column: span 2;
  background: rgba(255, 255, 255, 0.05);
}

span.plus {
  grid-row: span 2;
  height: 100%;
}

span.equal {
  background: rgba(255, 255, 255, 0.05);
}

.calculator span:hover {
  background: rgba(255, 255, 255, 0.1);
  transition: background 0.15s ease-in-out;
}

.calculator span:active {
  background: #14ff47;
  color: #192f00;
  font-size: 1.6rem;
  font-weight: 500;
}

.value::placeholder {
  color: rgb(255, 255, 255);
  opacity: 0.3;
}

@media (max-width: 600px) {
  .container {
    width: 95vw; /* fill almost whole width */
    padding: 0.4rem 0.4rem;
  }

  .calculator {
    grid-auto-rows: 75px;
  }

  .value {
    font-size: 2rem;
    height: 120px;
    padding: 12px;
  }

  .calculator span {
    font-size: 1.3rem;
  }
}

@media (max-width: 400px) {
  .container {
    width: 98vw;
    padding: 0.3rem 0.3rem;
  }

  .calculator {
    grid-auto-rows: 65px;
  }

  .value {
    font-size: 1.7rem;
    height: 100px;
    padding: 10px;
  }

  .calculator span {
    font-size: 1.1rem;
  }
}