While toying around with some font sizes on my persona ikiwiki I discovered that some font sizes in the default CSS are fixed rather than relative. Here's a git patch that replaces them with relative font sizes (assuming the default 12pt/16px base font size recommended by the W3C): 
From 01c14db255bbb727d8dd1e72c3f6f2f25f07e757 Mon Sep 17 00:00:00 2001
From: Giuseppe Bilotta <giuseppe.bilotta@gmail.com>
Date: Tue, 17 Aug 2010 00:48:24 +0200
Subject: [PATCH] Use relative font-sizes

---
 doc/style.css |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/doc/style.css b/doc/style.css
index 66d962b..fa4b2a3 100644
--- a/doc/style.css
+++ b/doc/style.css
@@ -14,7 +14,7 @@ nav {
 
 .header {
 	margin: 0;
-	font-size: 22px;
+	font-size: 140%;
 	font-weight: bold;
 	line-height: 1em;
 	display: block;
@@ -22,7 +22,7 @@ nav {
 
 .inlineheader .author {
 	margin: 0;
-	font-size: 18px;
+	font-size: 112%;
 	font-weight: bold;
 	display: block;
 }
-- 
1.7.2.rc0.231.gc73d