I looked at http://why-is-a-raven-like-a-writing-desk.com/ and I see that the main site title is “why is a raven like a writing desk?” and the first content heading is “48 hour wine trail. Sonoma Valley. A Photo-journey.” Both are already bold.
To change the site title to italic, you could add this to your Appearance > Customize > CSS editor:
#site-title a {
font-style: italic
}
To change content headings to italic, add this:
.entry-title,
.entry-title a {
font-style: italic
}
To learn more about how to find which selectors to use, check out this guide: