:root {
  --primary-color: rgba(45, 52, 57, 0.877);
  --secondary-color: rgb(54, 61, 64);
  --text-color: rgb(255, 255, 255);
  --border-radius: 7px;
}

* {
  box-sizing: border-box;
  font-family: "Segoe UI", Tahoma, Geneva, Verdana, sans-serif;
  font-weight: normal;
}

body {
  padding: 0;
  margin: 0;
  background: rgba(26, 34, 39, 0.808);
  overflow: hidden;
}

.calculator-grid {
  width: 100%;
  margin: auto;
  position: relative;
  display: grid;
  justify-content: center;
  align-content: center;
  grid-template-columns: repeat(4, 120px);
  grid-template-rows: minmax(220px, auto) repeat(6, 90px);
  min-height: 100vh;
}

.calculator-grid > button {
  background-color: var(--primary-color);
  color: var(--text-color);
  font-size: 1.5rem;
  border: 1.5px solid rgba(0, 0, 0, 0.336);
  cursor: pointer;
  user-select: none;
  border-radius: var(--border-radius);
}

/* disabled */
.calculator-grid > button.disabled {
  background-color: rgba(26, 34, 39, 0.671) !important;
  color: #666666;
  cursor: auto;
  pointer-events: none;
}

.calculator-grid > button:hover {
  background-color: var(--secondary-color);
}

.calculator-grid > button[data-number],
.calculator-grid > button[data-positivenegative] {
  background-color: var(--secondary-color);
}

.calculator-grid > button[data-number]:hover,
.calculator-grid > button[data-positivenegative]:hover {
  background-color: var(--primary-color);
}

.calculator-grid > button[data-equals] {
  background-color: rgb(76, 194, 255);
  color: #000;
}

.calculator-grid > button[data-equals]:hover {
  background-color: rgb(71, 177, 232);
}

.span-two {
  grid-column: span 2;
}

/* output display */
.output {
  background-color: rgba(26, 34, 40, 0.911);
  position: relative;
  grid-column: 1 / -1;
  display: flex;
  align-items: flex-end;
  justify-content: space-around;
  flex-direction: column;
  padding: 10px;
  word-wrap: break-word;
  word-break: break-all;
  border-radius: var(--border-radius);
}

.output.disabled::after {
  content: "";
  background-color: rgba(0, 0, 0, 0.5);
  border-radius: var(--border-radius);
  position: absolute;
  top: 0;
  left: 0;
  bottom: 0;
  right: 0;
}

.output .previous-operand {
  color: rgba(255, 255, 255, 0.75);
  font-size: 1.5rem;
  user-select: none;
}

.output .current-operand {
  color: white;
  font-size: 4rem;
}

/* history icon */
.output div#history-icon i {
  position: absolute;
  display: inline-block;
  top: 10px;
  left: 10px;
  color: white;
  user-select: none;
}

/* history icon tooltip */
.output div#history-icon span.tooltiptext {
  background-color: rgb(46, 46, 46);
  position: absolute;
  left: 35px;
  top: 10px;
  font-size: 11px;
  color: #fff;
  text-align: center;
  padding: 6px;
  border-radius: 5px;
  z-index: 1;
  visibility: hidden;
  opacity: 0;
  transition: opacity 0.3s ease;
}

/* hover tooltip */
.output div#history-icon:hover span.tooltiptext {
  visibility: visible;
  opacity: 1;
}

/* history section */
[data-history] {
  position: absolute;
  background-color: rgb(32, 32, 32);
  grid-column: 1 / -1;
  grid-row: 1 / -1;
  color: white;
  font-size: 1.1rem;
  padding: 10px;
  min-width: 30rem; /*480px*/
  height: 0rem;
  line-height: 2;
  word-wrap: break-word;
  word-break: break-all;
  border-radius: var(--border-radius);
  overflow-y: auto;
  bottom: 0%;
  transition: all 0.3s ease;
  visibility: hidden;
  user-select: none;
}

/* show history class */
.show {
  bottom: 0;
  height: 33.75rem; /*600px*/
  visibility: visible;
  user-select: auto;
}

/* history section scrollbar */
::-webkit-scrollbar {
  width: 2px;
}

::-webkit-scrollbar-track {
  display: none;
}

::-webkit-scrollbar-thumb {
  background-color: #888;
  height: 200px;
}

/* media queary */
@media (max-width: 490px) {
  .calculator-grid {
    grid-template-columns: repeat(4, 80px);
    grid-template-rows: minmax(130px, auto) repeat(6, 70px);
  }

  .output {
    justify-content: space-around;
    padding: 0 10px;
  }

  .output .previous-operand {
    font-size: 1rem;
  }

  .output .current-operand {
    font-size: 2.4rem;
  }

  [data-history] {
    font-size: 1rem;
    min-width: 20rem;
    height: 0rem;
  }

  .show {
    height: 26.2rem;
    bottom: 0;
    visibility: visible;
    user-select: auto;
  }
}