Because that defeats the purpose of using CSS to separate your styles from your markup. Set the style once in a stylesheet and it will apply to every instance of that class, id, element or whatever throughout your site. If you decide to change your styles, you only need to change it in one place. Using inline styles means you have to go through the entire site for every change and makes it a nightmare to maintain.
Use the W3C valuidators for [HTML and [URL="http://jigsaw.w3.org/css-validator/"]CSS](http://validator.w3.org). They'll alert you to invalid code, including typos - although it may take a little practice to get used to interpreting the results. "Parse error" in the CSS validator very often means something like you have here - a colon instead of a semi-colon, no closing bracket or something like that. If you need help with it, feel free to post back here.