* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
  font-family: 'Segoe UI', sans-serif;
}

body {
  height: 100vh;
  display: flex;
  align-items: center;
  justify-content: center;
  background: linear-gradient(135deg, #667eea, #8f8fd9, #5fa8a7, #185a9d);
  background-size: 300% 300%;
  animation: gradient-move 10s ease-in-out infinite;
}

@keyframes gradient-move {
  0% {
    background-position: 0% 50%;
  }
  50% {
    background-position: 100% 50%;
  }
  100% {
    background-position: 0% 50%;
  }
}

.container {
  width: 100%;
  max-width: 400px;
}

.calculator {
  background: rgba(255, 255, 255, 0.15);
  backdrop-filter: blur(15px);
  padding: 20px;
  border-radius: 20px;
  box-shadow: 0 8px 32px rgba(0, 0, 0, 0.3);
  animation: calc-fade-in 0.8s cubic-bezier(0.23, 1, 0.32, 1);
  transform: scale(0.95);
  opacity: 0;
  animation-fill-mode: forwards;
}

@keyframes calc-fade-in {
  0% {
    opacity: 0;
    transform: scale(0.8);
  }
  100% {
    opacity: 1;
    transform: scale(1);
  }
}

.display {
  background-color: rgba(255, 255, 255, 0.1);
  color: #fff;
  text-align: right;
  padding: 20px;
  border-radius: 12px;
  font-size: 2rem;
  margin-bottom: 20px;
  word-wrap: break-word;
  min-height: 60px;
  transition: background-color 0.4s, color 0.4s;
}

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

button {
  padding: 20px;
  font-size: 1.2rem;
  border: none;
  border-radius: 12px;
  background-color: rgba(255, 255, 255, 0.2);
  color: white;
  cursor: pointer;
  transition: background 0.2s ease, transform 0.1s;
}

button:hover {
  background-color: rgba(255, 255, 255, 0.35);
  transform: scale(1.07);
}

button:active {
  background-color: rgba(255, 255, 255, 0.5);
  color: #764ba2;
  transform: scale(0.96);
}