How to add a new Google font.
The list of all Google Fonts available in the theme is in wp-content/themes/mariana-handmade/includes/lists.php file, starting from line 855:
So in order to add a new font, please duplicate this line, for example:
'Advent Pro' => array('family'=>'sans-serif'),
replacing 'Advent Pro' with the title of the font you would like to add. Then save the file.