HTML style tweaks:
- for Internet Explorer 11, hide the browser's own
'clear' button on input fields to prevent an ugly
display problem where IE's clear button overlaps
our own button.
- make the border around <programlisting> tags
just a touch lighter/less constrasty.
- make <replaceable> content within <filename>
tags inherit the <filename> color.
- provide styling to help fix a vertical alignment
issue when including "thumb" graphics in a
paragraph.
Documents that could use this fix need to change
the <para> tag to <para condition="thumb">.