Re: CSS file for texinfo HTML output

[Gavin Smith]

On 26 January 2016 at 23:47, Karl Berry <address@hidden> wrote:
>
> In the alternative, if you feel you must override font sizes for some
> crazy reason, at least use pt or em instad of px.  px measurements,
> except when related to something actually pixel-based, like image size,
> are bad, because they do not adjust to the user's display environment.
> Your pixel is not the same as my pixel is not the same as ...

Most of the advice I found on the web a few weeks ago on this issue
said the opposite, and to use px instead of pt, and only to use pt if
it was being printed on paper, although I didn't really understand
why.

For reference, here's the CSS standard on the definition of a pixel:

===

For lower-resolution devices, and devices with unusual viewing
distances, it is recommended instead that the anchor unit be the pixel
unit. For such devices it is recommended that the pixel unit refer to
the whole number of device pixels that best approximates the reference
pixel.

Note: Note that if the anchor unit is the pixel unit, the physical
units might not match their physical measurements. Alternatively if
the anchor unit is a physical unit, the pixel unit might not map to a
whole number of device pixels.

Note: Note that this definition of the pixel unit and the physical
units differs from previous versions of CSS. In particular, in
previous versions of CSS the pixel unit and the physical units were
not related by a fixed ratio: the physical units were always tied to
their physical measurements while the pixel unit would vary to most
closely match the reference pixel. (This change was made because too
much existing content relies on the assumption of 96dpi, and breaking
that assumption breaks the content.)

The reference pixel is the visual angle of one pixel on a device with
a pixel density of 96dpi and a distance from the reader of an arm’s
length. For a nominal arm’s length of 28 inches, the visual angle is
therefore about 0.0213 degrees. For reading at arm’s length, 1px thus
corresponds to about 0.26 mm (1/96 inch).

===

http://www.w3.org/TR/css3-values/#absolute-lengths