@import url("https://fonts.googleapis.com/css2?family=League+Spartan:wght@400;600;700&display=swap");

:root {
  --border-radius: 8px;
  --main-background-color: hsl(222, 26%, 31%);
  --keypad-background-color: hsl(223, 31%, 20%);
  --screen-background-color: hsl(224, 36%, 15%);
  --del-reset-key-bg-color: hsl(225, 21%, 49%);
  --del-reset-key-bg-color-hover: hsl(224, 76%, 80%);
  --del-reset-key-shadow-color: hsl(224, 28%, 35%);
  --equal-key-bg-color: hsl(6, 63%, 50%);
  --equal-key-bg-color-hover: hsl(6, 99%, 67%);
  --equal-key-shadow-color: hsl(6, 70%, 34%);
  --key-bg-color: hsl(30, 25%, 89%);
  --key-bg-color-hover: hsl(0, 0%, 100%);
  --key-shadow-color: hsl(28, 16%, 65%);
  --text-color: hsl(0, 0%, 100%);
  --text-color-num: hsl(221, 14%, 31%);
  --text-color-prev-op: #ccc;
  --text-color-equal-btn: hsl(0, 0%, 100%);
}

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

html {
  font-size: 62.5%; /* 1rem = 10px */
}

body {
  min-height: 100vh;
  background-color: var(--main-background-color);
  display: flex;
  justify-content: center;
  align-items: center;
  font-family: "League Spartan", sans-serif;
  transition: background-color 0.5s;
}

.container {
  width: 90%;
  max-width: 45rem;
  padding: 4rem;
}

.calc-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 1.6rem;
  position: relative;
}

.theme-number {
  width: 4rem;
  position: absolute;
  top: -1.1rem;
  right: 0.7rem;
  display: flex;
  justify-content: space-between;
}

.theme-number span {
  font-weight: 600;
  color: var(--text-color);
}

.calc-text {
  color: var(--text-color);
  font-size: 2.4rem;
  font-weight: bold;
  padding-left: 0.6rem;
}

.calc-theme {
  display: flex;
  width: 11rem;
  justify-content: space-between;
  align-items: center;
}

.calc-theme span {
  color: var(--text-color);
  font-weight: bold;
  text-transform: uppercase;
  font-size: 1rem;
  margin-left: 1rem;
}

.tri-state-toggle {
  display: flex;
  align-items: center;
  justify-content: space-evenly;
  width: 5.5rem;
  height: 2rem;
  border-radius: 1.5rem;
  background-color: var(--keypad-background-color);
}

.toggle-btn {
  width: 1.2rem;
  height: 1.2rem;
  border: none;
  outline: none;
  border-radius: 50%;
  cursor: pointer;
  position: relative;
  opacity: 0;
}

.active {
  opacity: 1;
  background-color: var(--equal-key-bg-color);
}

.active:hover {
  background-color: var(--equal-key-bg-color-hover);
}

.calc-display {
  width: 100%;
  min-height: 11rem;
  display: flex;
  flex-direction: column;
  justify-content: space-around;
  align-items: flex-end;
  padding: 1rem;
  color: var(--text-color);
  background-color: var(--screen-background-color);
  margin-bottom: 1.2rem;
  border-radius: var(--border-radius);
  font-size: 3rem;
  font-weight: bold;
  word-break: break-all;
}

.prev-op {
  color: var(--text-color-prev-op);
  font-size: 2.2rem;
}

.calc-body {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  padding: 2rem;
  background-color: var(--keypad-background-color);
  border-radius: var(--border-radius);
  gap: 1.8rem;
}

.calc-op-box {
  font-family: inherit;
  padding: 1rem 0;
  text-align: center;
  background-color: var(--key-bg-color);
  border-radius: var(--border-radius);
  box-shadow: 0 2.5px var(--key-shadow-color);
  border: none;
  outline: none;
}

.calc-op-box:hover {
  cursor: pointer;
  background-color: var(--key-bg-color-hover);
}

.calc-op-box span {
  font-weight: bold;
  font-size: 2.8rem;
  color: var(--text-color-num);
}

.btn {
  color: #fff;
  font-family: inherit;
  text-align: center;
  border-radius: var(--border-radius);
  padding: 1.2rem 0;
  border: none;
  font-weight: bold;
  font-size: 2rem;
  text-transform: uppercase;
  cursor: pointer;
}

.btn-del,
.btn-reset {
  background-color: var(--del-reset-key-bg-color);
  box-shadow: 0 2.5px var(--del-reset-key-shadow-color);
}
.btn-reset {
  grid-column: span 2;
}

.btn-del:hover,
.btn-reset:hover {
  background-color: var(--del-reset-key-bg-color-hover);
}

.btn-equal {
  color: var(--text-color-equal-btn);
  background-color: var(--equal-key-bg-color);
  box-shadow: 0 2.5px var(--equal-key-shadow-color);
  grid-column: span 2;
}

.btn-equal:hover {
  background-color: var(--equal-key-bg-color-hover);
}

@media (max-width: 600px) {
  html {
    font-size: 56.25%;
  }

  .container {
    width: 100%;
    padding: 4rem 3rem;
  }

  .calc-body {
    gap: 1.8rem 1.2rem;
  }

  .calc-op-box {
    padding: 1.6rem 0rem;
    border-radius: 5px;
  }
}