/* Root Variables for Premium Glassmorphism Theme with Water Drop Effect */
:root {
  --primary-bg: linear-gradient(135deg, #1b1b1b, #2e2e2e, #3f3f3f);
  --glass-bg: rgba(255, 255, 255, 0.09);
  --glass-border: rgba(255, 255, 255, 0.18);
  --text-color: #00eaff;
  --shadow-color: rgba(0, 255, 255, 0.5);
  --button-bg: rgba(255, 255, 255, 0.15);
  --button-hover: rgba(255, 255, 255, 0.25);
  --special-btn-bg: rgba(255, 0, 89, 0.4);
  --special-btn-hover: rgba(255, 0, 89, 0.6);
  --equal-btn-bg: rgba(0, 255, 126, 0.4);
  --equal-btn-hover: rgba(0, 255, 126, 0.6);
  --operator-btn-bg: rgba(24, 220, 255, 0.4);
  --operator-btn-hover: rgba(24, 220, 255, 0.6);
}

/* Water Drop Background Effect */
body::before {
  content: "";
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  background: url('https://www.transparenttextures.com/patterns/water.png');
  opacity: 0.15;
  pointer-events: none;
}

/* Water Drop Animation */
@keyframes waterDrop {
  0% {
    transform: translateY(-10px) scale(1);
    opacity: 0.6;
  }
  50% {
    transform: translateY(0) scale(1.05);
    opacity: 1;
  }
  100% {
    transform: translateY(5px) scale(1);
    opacity: 0.6;
  }
}

/* Reset */
* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
  user-select: none;
}

body {
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh;
  background: var(--primary-bg);
  font-family: "Inter", "Poppins", "Montserrat", sans-serif;
}

/* Glassmorphism Calculator */
.calculator {
  width: 400px;
  padding: 30px;
  border-radius: 20px;
  background: var(--glass-bg);
  border: 2px solid var(--glass-border);
  backdrop-filter: blur(22px);
  box-shadow: 0px 12px 35px rgba(0, 0, 0, 0.7);
  animation: fadeIn 1s ease-in-out;
}

@keyframes fadeIn {
  from {
    opacity: 0;
    transform: scale(0.9);
  }
  to {
    opacity: 1;
    transform: scale(1);
  }
}

/* Input Field */
.input input {
  width: 100%;
  height: 90px;
  font-size: 36px;
  text-align: right;
  padding: 15px;
  border: none;
  outline: none;
  border-radius: 15px;
  background: rgba(255, 255, 255, 0.15);
  color: var(--text-color);
  font-weight: bold;
  margin-bottom: 25px;
  box-shadow: inset 0px 4px 14px var(--shadow-color);
  backdrop-filter: blur(22px);
  animation: slideIn 0.6s ease-in-out;
}

@keyframes slideIn {
  from {
    transform: translateY(-20px);
    opacity: 0;
  }
  to {
    transform: translateY(0);
    opacity: 1;
  }
}

/* Button Grid */
.buttons {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 15px;
}

/* Button Styling */
button {
  padding: 20px;
  font-size: 26px;
  font-weight: bold;
  border: none;
  border-radius: 12px;
  cursor: pointer;
  background: var(--button-bg);
  color: var(--text-color);
  transition: all 0.3s ease;
  box-shadow: 0px 6px 18px var(--shadow-color);
  text-shadow: 0px 0px 8px var(--shadow-color);
  backdrop-filter: blur(16px);
  animation: popIn 0.4s ease-in-out;
}

@keyframes popIn {
  from {
    transform: scale(0.8);
    opacity: 0;
  }
  to {
    transform: scale(1);
    opacity: 1;
  }
}

/* Hover Effect */
button:hover {
  background: var(--button-hover);
  box-shadow: 0px 6px 26px var(--shadow-color);
  animation: waterDrop 0.6s ease-in-out;
}

/* Button Click Animation */
button:active {
  transform: translateY(5px) scale(0.94);
  box-shadow: 0px 0px 28px var(--shadow-color);
}

/* Special Buttons */
button:nth-child(1) {
  background: var(--special-btn-bg);
}
button:nth-child(1):hover {
  background: var(--special-btn-hover);
}

button:nth-child(2) {
  background: var(--operator-btn-bg);
}
button:nth-child(2):hover {
  background: var(--operator-btn-hover);
}

button:nth-child(19) {
  grid-column: span 2;
  background: var(--equal-btn-bg);
}
button:nth-child(19):hover {
  background: var(--equal-btn-hover);
}

/* Operator Buttons */
button[data-operator] {
  background: var(--operator-btn-bg);
}
button[data-operator]:hover {
  background: var(--operator-btn-hover);
}

/* Zero Button */
button.zero {
  grid-column: span 2;
}