I noticed that Web-kit browsers like Chrome and Safari (Windows) tend to round em values to nearest pixel, while Firefox, IE, ? Opera ? can use sub-pixel values. This is normally not a big issue, but when I use em to precisely align letter spacing or use text-shadows for consistent effect in different client resolutions this causes me headache. Take a look in the following test case.
You will see that in FF even the smallest letters still have a shadow, while Chrome rounds down the em value to zero and the first two paragraphs have no shadow.
EDIT This is not about the units. If you replace 0.03em with 0.9, 0.8, 0.7 .. px FF will display smaller and smaller shadow, while when Chrome goes below 1px it suddenly displays nothing.
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html lang="bg" xml:lang="bg" xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<style type="text/css">body {font-size: 18px;} p {color: cyan; text-shadow: -0.03em -0.03em 0 rgb(0, 0, 0);}</style>
</head>
<body>
<p style="font-size:1em">No Shadow Test</p>
<p style="font-size:1.5em">No Shadow Test</p>
<p style="font-size:2em">Test</p>
<p style="font-size:2.5em">Test</p>
<p style="font-size:3em">Test</p>
<p style="font-size:3.5em">Test</p>
<p style="font-size:4em">Test</p>
<p style="font-size:4.5em">Test</p>
<p style="font-size:5em">Test</p>
</body>
</html>
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