Views 3 List Style CSS
The only good way is to use the 'add a class'-option in views. That allows for maximum flexibility and should not break if something in the view changes. (block-view-id-something can break when numbers or names change).

One you have added a css class to the field, something like horizontal. Then you can define it in your theme file css with .horizontal {...}.

But since themes can update their css, overwriting your changes, you are even better off using an extra stylesheet in your themes folder. Give it any name you want, add the .horizontal {...} lines. Then open the *.info file in your theme and add stylesheets[all][] = &lt;stylename&gt;.css. 

If it might break after a style update, all you have to do is add this line again.