The taglines have special classes you could style.
Each tagline has a “tagline”
Each Top tagline has “top_tagline”
Each bottom tagline has “bottom_tagline”
If there is no tagline set, on some pages (E.g. on portfolio detail page) the title of the post is displayed. It has a class of “top_title”

.tagline {
    font-size: 40px !important;
}