Moving minor updates between local and live sites – just database?

If you only changed some CSS, then updating the CSS file on the live server should be sufficient (unless you need to clear a cache or something).

If you changed/created posts on your localhost – then those posts will not be on your live site. You could overwrite the live site’s database with your localhost database – however then you will lose any data that was created on the live site (for example, comments).

In general, if the posts/pages you’re creating on localhost are supposed to also be on the live site, you’re better off creating them there in the first place.