Visualize code that defines styles

## Problem
When multiple styles are defined with similar names, it's hard to quickly select the right style for the desirable effect or to determine if a style already exists. A lot of trial and error was observed in the UX study which involved styling text using predefined styles in [a dart file](https://github.com/InMatrix/veggieseasons/blob/master/lib/styles.dart).

## Proposal
Visualize styles in the code editor. Below is a mock-up of the concept: