Sometimes, themes cause problems with the way text is shown in forms and dropdowns in webpages. If one simple rule doesn't work for all sites, it maybe necessary to make site-specific rules.
If one is using Firefox, open and edit /home/your_name/.mozilla/firefox/********.default/chrome/userContent.css
as described here except that the actual matter to be added will depend on how the appearance of content of the web-page is to be modified.
For example:
@-moz-document domain("wolframalpha.com") {
INPUT, TEXTAREA {color: black !important; background: #aaaaaa !important; }
}
@-moz-document domain("askubuntu.com") {
INPUT, TEXTAREA {color: #aaaaaa !important; background: black !important; }
}
@-moz-document domain("google.com") {
INPUT, TEXTAREA {color: blue !important; background: tan !important; }
}
For the Chrome (or Chromium browser), the use of an extension is required. I prefer Stylish. This extension provides a GUI for making site-specific rules:
and
(Stylish is also available for Firefox!)