Say goodbye to pixel perfect layouts, and embrace flexible design principles
Using relative units to set text size presents problems for designers who would like to produce 'pixel-perfect' layouts on their Web pages. Absolute control of page layouts is impossible when using relative units; the resulting page will change according to the needs of the end user and the physical attributes of the display device.
The size of Web pages is never predictable; different sized monitors, different screen resolutions, resized browser windows, devices with small, large or medium screens. Unpredictability is the only constant.
And the technology people use to view web pages does not stand still. Reading Jeffrey Zeldman's excellent book, 'Designing with web standards' I was alerted to the fact that the first versions of the Safari browser for the Mac threw another variable into the mix - the default text size in Safari was not the same as the its competitors. Safari used 14 pixels as the default text size, rather than the 'standard' 16 pixels used by competing browsers (this has been addressed in later version of the browser).
Unless you are designing for a closed environment like an intranet and you can control screen size, resolution, and the habits and capabilities of your users, the stress free solution is to give up the idea that you can completely control how the Web page looks to your users.
A major plus-point of the web is that it is available, and works on a huge variety of client devices; that was a reason for its growth in the first place.
Play to the strengths of the medium; design web pages that are flexible enough to adapt to the needs of both the client device and the end user. And apply this general principle when setting the size of the text on the pages you design.
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