A window in Conkeror is a XUL document, commonly referred to as "chrome". Chrome includes such visual elements as the mode-line, the minibuffer, and the tab-bar. These elements can be styled with CSS.
You can use register_user_stylesheet in your rc script to add styles to the chrome:
register_user_stylesheet('file:///path/to/css/file');You can also include CSS directly in the Javascript file:
register_user_stylesheet(
"data:text/css,"+
escape("#minibuffer, .mode-line {"+
" font-size: 16px;"+
"}\n"+
"#minibuffer-prompt { color: red; }"));The above code sets the font-size of the minibuffer and the mode-line to 16px, and sets the font colour of the prompt to red.