Create sprites[-regular|-solid|-brands].css

+ CSS images are set by classes.
+ No CSS variables are used.
+ The type of image (i.e. *background, list-style* or *content*)
  is predefined for some (HTML) element and class combinations:

  * **(`dt`|`dd`|`li`)**`.fa`[`r`|`s`|`b`]*`-name`* use `list-style-image`
  * **`.i`**`.fa`[`r`|`s`|`b`]*`-name`* use `background-image`
  * **`.a`**`.fa`[`r`|`s`|`b`]*`-name`* use `content` *after* element content
  * **(`.b`|`i`)**`.fa`[`r`|`s`|`b`]*`-name`* use `content` *before* element content
  * **`summary`**`.fa`[`r`|`s`|`b`]*`-name`* use `content` for *marker* box