body {
  font-family: 'Roboto', sans-serif;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  height: 100vh;
  margin: 0;
  background-size: cover;
  background-position: center;
  user-select: none;
}
h1 {
  margin-bottom: 20px;
}
.number-row {
  display: flex;
  justify-content: center;
  margin-bottom: 10px;
}
.number {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 80px;
  height: 100px;
  margin: 0 5px;
  border-radius: 15%;
  cursor: pointer;
  user-select: none;
  position: relative;
  font-size: 32px;
  font-weight: bold;
  color: rgb(0, 0, 0);
  transition: opacity 0.3s, filter 0.3s;
}
.number.red {
  background-color: red;
}
.number.yellow {
  background-color: yellow;
}
.number.blue {
  background-color: rgb(68, 109, 221);
}
.number.used {
  filter: blur(2px);
  opacity: 0.1;
  pointer-events: none;
}
.button-container {
  display: flex;
  justify-content: center;
}
button {
  margin: 5px;
  padding: 10px 20px;
  font-size: 18px;
  cursor: pointer;
  border: 1px solid rgba(0, 0, 0, 0.2);
  border-radius: 5px;
  background-color: transparent;
  transition: all 0.3s;
}
button.reset:hover {
  border-color: red;
  background-color: rgba(255, 0, 0, 0.1);
}
button.undo:hover {
  border-color: green;
  background-color: rgba(0, 255, 0, 0.1);
}

@media (max-width: 768px) {
  .number {
    width: 40px;
    height: 50px;
    font-size: 16px;
  }
}