html,
body {
  margin: 0;
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  min-height: 100vh;
}

header {
  display: flex;
  flex-direction: column;
  align-items: center;
}

#result-display {
  min-height: 20px;
}

button {
  margin: 10px;
  font-size: 40px;
  background-color: transparent;
  border: 1px solid rgba(0, 0, 0, 0.1);
  width: 100px;
  height: 100px;
  border-radius: 50%;
}

button:hover {
  border: 1px solid rgba(0, 0, 0, 0.5);
  cursor: pointer;
}