There are several steps to customising a theme in spacemacs, with some parallells to customising
the standard emacs build. 

    The GUI elements typically relevant to customizing spacemancs appearance are: 
        1. Colour themes 
        2. Fonts & Icons 
        3. Modelines
        4. Frame styling and layouts 
    
    Colour themes are the easiest and most direct configuration option. You can set
    the theme to another inside of your '.spacemacs' file, under 'user-init()'
    to one of the default pre-installed themes. 
    
    The shortcut 'SPC T n' will switch to the "next" theme for previewing, and the 
    'SPC T s' will select it to be applied. 
    
    The relevant documentation page that covers the basics being available at: 
    https://develop.spacemacs.org/doc/DOCUMENTATION.html#gui-elements
    
    I have also provided a more straight-forward list of examples and references, if 
    you just want something to paste: https://git.io/Jcc96