body {
  display: flex;
  flex-direction: column;
  align-items: center;
  font-family: sans-serif;
  margin: 0;
  padding: 0;
  background: #f0f0f0;
}

header {
  margin: 20px;
}

header h1 {
  font-size: 2em;
  margin: 0;
}

#toolbar {
  display: flex; /* horizontal layout */
  align-items: center;
  margin-bottom: 10px;
  flex-wrap: wrap; /* wrap on smaller screens */
}

.color-btn {
  width: 30px;
  height: 30px;
  border: 2px solid #333;
  cursor: pointer;
  margin-right: 5px;
}

#erase-btn {
  padding: 5px 10px;
  cursor: pointer;
  margin-left: 10px;
}

#board {
  border: 2px solid #333;
  background: #fff;
  touch-action: none;
  margin-bottom: 20px;
}

footer {
  margin: 20px;
}