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

body, html {
  width: 100%;
  height: 100%;
  font-family: 'Segoe UI', sans-serif;
  background: #f4f4f9;
  display: flex;
  flex-direction: column;
  align-items: center;
}

header {
  padding: 1rem;
  text-align: center;
  background-color: #3f51b5;
  color: white;
  width: 100%;
  box-shadow: 0 2px 4px rgba(0,0,0,0.2);
}

main {
  flex-grow: 1;
  display: flex;
  align-items: center;
  justify-content: center;
  width: 100%;
}

.calculator {
  background: white;
  padding: 1rem;
  border-radius: 12px;
  box-shadow: 0 4px 8px rgba(0,0,0,0.1);
  max-width: 360px;
  width: 100%;
}

#display {
  width: 100%;
  height: 3rem;
  font-size: 1.5rem;
  text-align: right;
  padding: 0.5rem;
  margin-bottom: 1rem;
  border: 1px solid #ddd;
  border-radius: 8px;
}

.buttons {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 0.5rem;
}

button {
  padding: 1rem;
  font-size: 1.2rem;
  background-color: #e0e0e0;
  border: none;
  border-radius: 8px;
  transition: background-color 0.2s;
}

button:hover {
  background-color: #d0d0d0;
}

button.zero {
  grid-column: span 2;
}

.ad-container {
  width: 100%;
  margin: 1rem auto;
  text-align: center;
}

.bottom-ad {
  margin-bottom: 2rem;
}

.faq-section h2 {
  color: #3f51b5;
}

footer {
  background: #3f51b5;
  color: white;
  text-align: center;
  padding: 1rem;
  margin-top: 2rem;
  width: 100%;
}