Changing the look of your webmail is simple. Once logged in, look for Theme at the bottom of the folder pane:

Once selected, the following interface will open from the bottom of the screen:

A number of options are available here. Beginning with layout, you will have the additional option of displaying a Clean interface, which looks like this:

Additionally, you will have the option to display message in Widescreen (displays the messages and message contents in two seperate columns) or Tallscreen, which displays messages in two rows.

Finally, the option is also available to customize the general spacing of items, from Compact to Spacious.