Use a reset stylesheet
Different browsers, and different versions of the same browser, have different default styles built in so will display the same web page differently.
The reset stylesheet sets up a consistent set of styles as a baseline across all browsers. You can then define your preferred styles to override the reset stylesheet.
Make sure the reset stylesheet is the first stylesheet your webpage references. Put your own preferred stylesheet after the reset stylesheet.
A good example is on Eric Meyer's website.
<html>
<head>
<link rel="stylesheet" type="text/css" href="css/reset.css" />
<link rel="stylesheet" type="text/css" href="css/yourProjectStyles.css" />
</head>
</html>
You may wish to use the W3 default stylesheet to give a reasonable style to your web pages. Add the stylesheet after the reset stylesheet and before your own stylesheets.