About cli themesSource:
CLI elements can be styled via a CSS-like language of selectors and properties. Only a small subset of CSS3 is supported, and a lot visual properties cannot be implemented on a terminal, so these will be ignored as well.
The style of an element is calculated from themes from four sources. These form a stack, and the themes on the top of the stack take precedence, over themes in the bottom.
The cli package has a built-in theme. This is always active. See
When an app object is created via
start_app(), the caller can specify a theme, that is added to theme stack. If no theme is specified for
start_app(), the content of the
cli.themeoption is used. Removed when the corresponding app stops.
The user may specify a theme in the
cli.user_themeoption. This is added to the stack after the app's theme (step 2.), so it can override its settings. Removed when the app that added it stops.
A theme is a named list of lists. The name of each entry is a CSS selector. Only a subset of CSS is supported:
Type selectors, e.g.
Class selectors, e.g.
.indexselects any element that has a class of "index".
#tocwill match the element that has the ID "toc".
The descendant combinator, i.e. the space, that selects nodes that are descendants of the first element. E.g.
div spanwill match all
<span>elements that are inside a
The content of a theme list entry is another named list, where the
names are CSS properties, e.g.
margin-left, and the list entries themselves define the values of
the properties. See
simple_theme() for examples.
For flexibility, themes may also define formatter functions, with
fmt. These will be called once the other styles are
applied to an element. They are only called on elements that produce
output, i.e. not on container elements.
Right now only a limited set of properties are supported. These include
left, right, top and bottom margins, background and foreground colors,
bold and italic fonts, underlined text. The
properties are supported to insert text before and after the
content of the element.
The current list of properties:
after: A string literal to insert after the element. It can also be a function that returns a string literal. Supported by all inline elements, list items, alerts and rules.
background-color: An R color name, or HTML hexadecimal color. It can be applied to most elements (inline elements, rules, text, etc.), but the background of containers is not colored properly currently.
before: A string literal to insert before the element. It can also be a function that returns a string literal. Supported by all inline elements, list items, alerts and rules.
class-map: Its value can be a named list, and it specifies how R (S3) class names are mapped to cli class names. E.g.
list(fs_path = "file")specifies that
fs_pathobjects (from the fs package) should always print as
.fileobjects in cli.
color: Text color, an R color name or a HTML hexadecimal color. It can be applied to most elements that are printed.
collapse: Specifies how to collapse a vector, before applying styling. If a character string, then that is used as the separator. If a function, then it is called, with the vector as the only argument.
digits: Number of digits after the decimal point for numeric inline element of class
fmt: Generic formatter function that takes an input text and returns formatted text. Can be applied to most elements. If colors are in use, the input text provided to
fmtalready includes ANSI sequences.
"italic"then the text is printed as cursive.
"bold", then the text is printed in boldface.
line-type: Line type for
list-style-type: String literal or functions that returns a string literal, to be used as a list item marker in un-ordered lists.
padding-right: This is currently used the same way as the margins, but this might change later.
start: Integer number, the first element in an ordered list.
string_quote: Quoting character for inline elements of class
"underline", then underlined text is created.
text-exdent: Amount of indentation from the second line of wrapped text.
transform: A function to call on glue substitutions, before collapsing them. Note that
transformis applied prior to implementing color via ANSI sequences.
vec_last: The last separator when collapsing vectors.
vec_sep: The separator to use when collapsing vectors.
vec_trunc: Vectors longer than this will be truncated. Defaults to 100.
More properties might be added later. If you think that a property is not applied properly to an element, please open an issue about it in the cli issue tracker.