响应式修饰符
Just the Docs 间距可与各种修饰符配合使用，让恁能够响应式地定位特定屏幕尺寸。将这些修饰符与间距配合使用，并显示前缀和后缀类。
| Modifier | Screen size |
|---|
| (none) | All screens until the next modifier |
xs | 320px (20rem) and up |
sm | 500px (31.25rem) and up |
md | 740px (46.25rem) and up |
lg | 1120px (70rem) and up |
xl | 1400px (87.5rem) and up |