Two modes over one document
The canvas and the code pane are two views of one reducer. Dragging a box and typing left: 40px reach the same action, so neither view is an export of the other. Markup commits on Apply — half-typed markup is invalid markup, and parsing per keystroke would churn the tree through garbage states and destroy the selection on every character. The stylesheet applies live, because a browser simply ignores a bad declaration.
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