:root {
  --bg-gradient-start: #e06963;
  --bg-gradient-end: #0c0f3f;
  --calculator-bg: #121328;
  --display-text-color: #ffffff;
  --display-placeholder-color: #9490ac;
  --button-text-color: #ffffff;
  --button-hover-shadow: 0 8px 25px #82899a;
  --equal-button-bg: #f9544c;
  --operator-button-color: #f9544c;
  --button-bg: transparent;
  --theme-switcher-bg: #333;
  --theme-switcher-slider: #fff;
}

[data-theme="light"] {
  --bg-gradient-start: #f0f2f5;
  --bg-gradient-end: #d9e2ec;
  --calculator-bg: #ffffff;
  --display-text-color: #22252d;
  --display-placeholder-color: #6b6b6b;
  --button-text-color: #22252d;
  --button-hover-shadow: 0 8px 25px rgba(0, 0, 0, 0.1);
  --equal-button-bg: #f9544c;
  --operator-button-color: #f9544c;
  --button-bg: #f7f7f7;
  --theme-switcher-bg: #ccc;
  --theme-switcher-slider: #fff;
}

* {
  padding: 0;
  margin: 0;
  box-sizing: border-box;
  font-family: "Roboto Mono", monospace;
}

body {
  height: 100vh;
  background: linear-gradient(to bottom, var(--bg-gradient-start) 0%, var(--bg-gradient-end) 100%);
  transition: background 0.3s ease;
  display: flex;
  justify-content: center;
  align-items: center;
}

.calculator {
  width: 356px;
  background-color: var(--calculator-bg);
  padding: 20px 30px 30px 30px;
  border-radius: 8px;
  box-shadow: 0 20px 50px rgba(173, 190, 255, 0.4);
  transition: background-color 0.3s ease;
}

.theme-switcher-container {
  display: flex;
  justify-content: flex-end;
  margin-bottom: 20px;
}

.switch {
  position: relative;
  display: inline-block;
  width: 50px;
  height: 24px;
}

.switch input {
  opacity: 0;
  width: 0;
  height: 0;
}

.slider {
  position: absolute;
  cursor: pointer;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  background-color: var(--theme-switcher-bg);
  transition: .4s;
}

.slider:before {
  position: absolute;
  content: "";
  height: 16px;
  width: 16px;
  left: 4px;
  bottom: 4px;
  background-color: var(--theme-switcher-slider);
  transition: .4s;
  z-index: 2;
}

.slider .fa-moon,
.slider .fa-sun {
    position: absolute;
    top: 50%;
    transform: translateY(-50%);
    font-size: 14px;
    color: #f1c40f;
    z-index: 1;
}

.slider .fa-moon {
    left: 5px;
}

.slider .fa-sun {
    right: 5px;
}

input:checked + .slider {
  background-color: var(--equal-button-bg);
}

input:checked + .slider:before {
  transform: translateX(26px);
}

.slider.round {
  border-radius: 34px;
}

.slider.round:before {
  border-radius: 50%;
}

.display {
  width: 100%;
}

.display input {
  width: 100%;
  padding: 15px 10px;
  text-align: right;
  border: none;
  background-color: transparent;
  color: var(--display-text-color);
  font-size: 35px;
  outline: none;
}

.display input::placeholder {
  color: var(--display-placeholder-color);
}

.buttons {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  grid-gap: 20px;
  margin-top: 40px;
}

.buttons button {
  font-size: 20px;
  padding: 17px;
  border: none;
  background-color: var(--button-bg);
  color: var(--button-text-color);
  cursor: pointer;
  border-radius: 5px;
  transition: box-shadow 0.2s ease;
}

.buttons button:hover {
  box-shadow: var(--button-hover-shadow);
}

.buttons button .fas {
  font-size: 18px;
}

button#equal {
  background-color: var(--equal-button-bg);
  color: #ffffff;
}

.operator {
    color: var(--operator-button-color);
}