How can I change the font-family of widgets' titles/headers?

To resolve this issue, you can log in to Dashboard > Customize > Font Selector, then select the font-family in the Heading Font.
Regards,

I can’t change the Japanese font by the way you suggested. Would you tell me how to change the font-family by customizing/adding css code?

I can’t change the Japanese font by the way you suggested. Would you tell me how to change the font-family by customizing/adding css code?

To resolve this issue, you can add the following code to the style.css file:

h1, h2, h3, h4, h5, h6, blockquote, .navbar .nav li a, .accordion .accordion-heading a, .news-slider .carousel-list .other-entry a, .nav-tabs a, .news-slider .carousel .carousel-inner .entry-category, .single .site-content > .hentry .post-categories li, .single .site-content > .hentry .entry-action .social-action .title-action, #dw_recentcomments .comment-title, #dw_recentcomments .comment-author {
    font-family: ...;
}

Note: You can find your font here: https://www.google.com/fonts
Regards,

Dominic, I need your further help!
I couldn’t find any Japanese font on Google Fonts. How can I apply a standard Japanese font (a font like “Arial” or “Verdana” of English font)?
I want to change each font-family of the title of a single post, the title and the contents (list of post titles) of widgets.
Also, it seems I can’t override the font-family of h1, h2, h3, and so on…