Themes are an encapsulation of reusable variables for consistent styling, represented as a
Themes can only be accessed within a style sheet when registered into Aesthetic. We can achieve
this using the
registerDefaultTheme() methods, both of which require a
unique name and an optional theme style sheet. A default theme can only
be defined twice, once for a light color scheme, the other for a dark color scheme.
Registration should happen near the root of the application, before any Aesthetic styled React component is imported or rendered.
The currently active theme can be changed programmatically by calling the
within in your application.