[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

@keyframes rainbowButton {
  0% { background-position: 0% 0%; }
  100% { background-position: -200% 0%; }
}
#barWorkspace {
  border-radius: 6px;
  background: linear-gradient(90deg, #FF6B6B, #FF7757, #FFAB3D, #6BF178, #6DD3FF, #D7B5FE, #FFB5E1, #FF6B6B);
  background-size: 1600% 100%;
  animation: rainbowButton 12s linear infinite;
  transition: filter 0.3s ease;
  & .toolbar__text {
    color: white;
    font-weight: 600;
  }
  & .toolbar__svg {
    display: none;
  }
  &:hover {
    filter: brightness(0.9);
  }
  &:active {
    filter: brightness(0.7);
  }
}
​