Add clear documentation for migrating from styled components with a theme

[jeremylynch]

Note a common feature used in Styled components is theming. I note #184 which introduces theming to this library. However, there is nothing in the documentation for this. Are we able to add createThemeProvider to the documentation?

[pancaspe87]

Hi @jeremylynch,

Thanks for reporting the missing info.

We have elected to not support theming (styled-components: Advanced Usage) in Compiled as the implementation complexity is high and the same affect can be achieved with CSS variables.

Documentation doesn't include some of the latest features and decisions; we'll try to update it asap.