A quick and simple way to boost font size is to unzip the attached file and drop it into your C:\Program Files\XMetaL 6.0\Author\DITA\XACs\ditabase folder. It's a bit of CSS code that will change the default font size from 14px to 16px.
Alternatively, you could add the following line to the end of the ditabase-base-override.css file that you already have:
$DOCUMENT {
font-size: 16px;
}
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