@layer
CSS 级联：
- Origin and Importance
- Inline Styles
- Layer
- Specificity
- Order of appearance
样式规则优先级：
- Important Browser Styles
- Important User Styles
- Important Developer Declarations
- Normal Developer Styles
- Normal User Styles
- Normal Browser Styles
layer 覆盖会忽略内部选择器权重
将第三方 css 分配给 layer: @import url(flickity.css) layer(vendors);