[css] SiYuan 按键彩虹渐变效果

实现 SiYuan 按键的彩虹渐变效果，参考了 https://siyuannote.com/docs/article/1724628228

更新：再次优化了颜色

#barWorkspace {
  border: none;
  background: none;
  width: 80px;
  height: 25px;
  cursor: pointer;
  border-radius: 8px;
  background: linear-gradient(90deg, #FF6B6B, #FF7757, #FFAB3D, #6BF178, #6DD3FF, #D7B5FE, #FFB5E1, #FF6B6B);
  background-size: 1600% 100%;
  animation: rainbowButton 12s linear infinite;
  user-select: none;
  transition: filter 0.3s ease;
  color: #FFF7EE;
  display: flex;
  align-items: center;
  justify-content: center;
  text-align: center;
  font-size: 12px;
  font-weight: bold;
}

#barWorkspace:hover {
  filter: brightness(0.8);
}

#barWorkspace:active {
  filter: brightness(0.7);
}

@keyframes rainbowButton {
  0% { background-position: 0% 0%; }
  100% { background-position: -200% 0%; }
}