It’s actually not quite as easy as a simple css change. Quark uses a 12 column grid. Currently for the header section, it uses 5 columns for the logo and 7 columns for the social icons and menu.
(if you haven’t seen it already, have a look at the demo site)
If you want to align the logo perfectly in the center, then you can remove the social icons & menu and extend the logo container to the full 12 columns. Alternatively, if you still need the menu, then you’d need to put the logo on a separate “row”.
All these changes would need to be done within header.php
.
For making simple text style changes, you’d need to update the styles in style.css
.
If you’re uncomfortable making html/php/css changes then I would highly recommend getting a developer to make them for you.