Graham bemethavinci
You can add any css you like in xtgem_templates.css
the preset templates use a variables system that allows you to 'tweak' the template from the 'Tweak colors for current template' option
setting this up is quite complex but do-able
when using xtgem_templates.css you can set different css for mobile or web using the xt_touch class
ie:
.class_name {...} for mobile devices
.xt_touch .class_name {...} for web devices
If you want certain classes to appear in the building tools 'class' selector
add those classes (or at least a dummy repeat of the class) to global_stylesheet.css
ie if you have a class .box {...} in xtgem_templates.css add .box {} in global_stylesheet.css and the class name will appear in the list
Note: the 'class' selector is fussy about a space between the class name and the {}
global_stylesheet.css is loaded after xtgem_templates.css
if you want to set your own blog css (standard non twig) then the preset templates are a good starting point