* {
  box-sizing: border-box;
  font-family: "Segoe UI", Roboto, sans-serif;
}

body {
  min-height: 100vh;
  margin: 0;
  display: flex;
  justify-content: center;
  align-items: center;
  background: linear-gradient(135deg, #ece9e6, #ffffff);
}

.container {
  background: #fff;
  padding: 2rem;
  border-radius: 1rem;
  box-shadow: 0 4px 15px rgba(0, 0, 0, 0.1);
  text-align: center;
  width: 320px;
}

h1 {
  margin-bottom: 1.5rem;
  font-size: 1.5rem;
  color: #333;
}

input[type="number"] {
  width: 100%;
  padding: 0.7rem 1rem;
  font-size: 1rem;
  border: 1px solid #ddd;
  border-radius: 0.5rem;
  margin-bottom: 1rem;
  transition: border 0.3s ease;
}

input[type="number"]:focus {
  border-color: #4a90e2;
  outline: none;
}

button {
  width: 100%;
  padding: 0.7rem 1rem;
  font-size: 1rem;
  background: #4a90e2;
  color: white;
  border: none;
  border-radius: 0.5rem;
  cursor: pointer;
  transition: background 0.3s ease, transform 0.1s ease;
}

button:hover {
  background: #357abd;
}

button:active {
  transform: scale(0.97);
}

#output {
  margin-top: 1.5rem;
  font-size: 1.3rem;
  font-weight: bold;
  color: #222;
  min-height: 2rem;
}

/* Tablet */
@media (max-width: 768px) {
  .container {
    width: 50%;
    padding: 1.5rem;
  }

  input[type="number"],
  button {
    font-size: 0.95rem;
    padding: 0.6rem 0.8rem;
  }

  h1 {
    font-size: 1.3rem;
  }

  #output {
    font-size: 1.2rem;
  }
}

/* Phone */
@media (max-width: 480px) {
  .container {
    width: 90%;
    padding: 1rem;
  }

  input[type="number"],
  button {
    font-size: 0.9rem;
    padding: 0.5rem 0.7rem;
  }

  h1 {
    font-size: 1.1rem;
  }

  #output {
    font-size: 1.1rem;
  }
}