Site-wide look and feel

Set the site-wide look and feel in the Site settings > Template > Template builder > Look and feel tab.  This video goes through look and feel basics.
 

Text

Text on your site is one of three types -- Heading 1, Heading 2, Body text.

Heading 1
This style is used for the Site name text, and is available on text pages as well.  It is typically the most visually prominent style.

Heading 2
This style is typically the second most visually prominent.

Body text
This style is used on text pages throughout the site.
 

Links

The Links style is used for all links on the site that are not part of the navigation.  These may be, for example, links to other websites, or a linked email address.
 

Navigation

The Navigation is the main list of pages.

For both the Links and the Navigation you can style the following states:

Plain
As the text normally appears

Mouseover
How the text appears when visitor moves their mouse over the text

Within the Navigation, you can also the style the Active navigation link.  This is the style of the link that represents the current page.  For example, if a visitor clicks on Paintings, then Paintings would become active.
 

Site style

These settings affect the appearance of all pages.

Background color
This is also the background color of some superimposed text.

Margin, Padding and Border styles
Think of an imaginary rectangle around your site.  This rectangle is the border.  Outside the rectangle is the margin, and inside the rectangle is the padding.
 

Icon style

The Small arrow style is usually used when arrows are close together.  The Large arrow style is used in the different Lightbox views, and around images in the Cycle and Carousel gallery layouts.
 

Custom CSS

Users knowledgeable in CSS can add it here.