* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}
html, body {
  width: 100vw;
  height: 100vh;
  background-size: cover;
  background-position: center;
  font-family: sans-serif;
  overflow: hidden;
}
.board {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  grid-template-rows: repeat(3, 1fr);
  width: 100vw;
  height: 100vh;
}
.cell {
  border: 1px solid #fff;
  display: flex;
  justify-content: center;
  align-items: center;
  font-size: 20vmin;
  color: white;
  user-select: none;
  cursor: pointer;
  transition: background-color 0.3s;
}
.cell:hover {
  background-color: rgba(255,255,255,0.1);
}
.status {
  position: absolute;
  top: 20px;
  left: 20px;
  color: white;
  font-size: 2rem;
  z-index: 10;
  text-shadow: 1px 1px 2px black;
}
.restart-btn {
  position: absolute;
  bottom: 20px;
  left: 20px;
  padding: 10px 20px;
  font-size: 1rem;
  border: none;
  background: white;
  color: black;
  border-radius: 10px;
  cursor: pointer;
  z-index: 10;
}
.background-picker {
  position: absolute;
  top: 20px;
  right: 20px;
  display: flex;
  gap: 10px;
  z-index: 10;
}
.background-picker img {
  width: 60px;
  height: 60px;
  border-radius: 5px;
  cursor: pointer;
  object-fit: cover;
  border: 2px solid white;
  transition: transform 0.2s;
}
.background-picker img:hover {
  transform: scale(1.1);
}