Text size is affected by multiple factors including browser default styles, styles added by the HTML document, browser settings, and sometimes user style sheets.

Gadgets for the Font Size on Blogger Pages. Blogger doesn't offer a gadget that allows users to change the font size -- while some users may require a larger font than others, it's not something ...

Decoded, that says “for an HTML page’s body section, the container for all the stuff you see on a page, set the font family to Arial and override everything else.” ...