21.3 HTML CSS

Cascading Style Sheets (CSS for short) is an Internet standard for influencing the display of HTML documents: see http://www.w3.org/Style/CSS/.

By default, makeinfo includes a few simple CSS commands to better implement the appearance of some Texinfo environments. Here is one of them, as an example:

pre.display { font-family:inherit }

A full explanation of CSS is (far) beyond this manual; please see the reference above. In brief, however, the above tells the web browser to use the same font as the main document for @display. By default, the HTML ‘<pre>’ command uses a monospaced font.

You can influence the CSS in the HTML output with two makeinfo options: --css-include=file and --css-ref=url.

The option --css-ref=url adds to each output HTML file a ‘<link>’ tag referencing a CSS at the given url. This allows using external style sheets. You may find the file texi2html/examples/texinfo-bright-colors.css useful for visualizing the CSS elements in Texinfo output.

The option --css-include=file includes the contents file in the HTML output, as you might expect. However, the details are somewhat tricky, as described in the following, to provide maximum flexibility.

The CSS file may begin with so-called ‘@import’ directives, which link to external CSS specifications for browsers to use when interpreting the document. Again, a full description is beyond our scope here, but we’ll describe how they work syntactically, so we can explain how makeinfo handles them.

There can be more than one ‘@import’, but they have to come first in the file, with only whitespace and comments interspersed, no normal definitions. (Technical exception: a ‘@charset’ directive may precede the ‘@import’’s. This does not alter makeinfo’s behavior, it just copies the ‘@charset’ if present.) Comments in CSS files are delimited by ‘/* ... */’, as in C. An ‘@import’ directive must be in one of these two forms:

@import url(http://example.org/foo.css);
@import "http://example.net/bar.css";

As far as makeinfo is concerned, the crucial characters are the ‘@’ at the beginning and the semicolon terminating the directive. When reading the CSS file, it simply copies any such ‘@’-directive into the output, as follows:

• If file contains only normal CSS declarations, it is included after makeinfo’s default CSS, thus overriding it.
• If file begins with ‘@import’ specifications (see below), then the ‘import’’s are included first (they have to come first, according to the standard), and then makeinfo’s default CSS is included. If you need to override makeinfo’s defaults from an ‘@import’, you can do so with the ‘! important’ CSS construct, as in:

  pre.example { font-size: inherit ! important }
  

• If file contains both ‘@import’ and inline CSS specifications, the ‘@import’’s are included first, then makeinfo’s defaults, and lastly the inline CSS from file.
• Any @-directive other than ‘@import’ and ‘@charset’ is treated as a CSS declaration, meaning makeinfo includes its default CSS and then the rest of the file.

If the CSS file is malformed or erroneous, makeinfo’s output is unspecified. makeinfo does not try to interpret the meaning of the CSS file in any way; it just looks for the special ‘@’ and ‘;’ characters and blindly copies the text into the output. Comments in the CSS file may or may not be included in the output.

In addition to the possibilities offered by CSS, makeinfo has many user-definable customization variables with which you can influence the HTML output. See Customization Variables.