Hello, can you provide more information about how you are running the sample? I can't reproduce this issue. Here are the steps I followed:
1. cd blockly-samples/examples/blockly-react
2. npm install --force (we have some peer dependency issues we should fix, but they don't matter for this demo)
3. npm run start
The browser opens and the React demo is displayed correctly. Please provide more information and we'll try to help you.
As a related note, you might want to check out the
react-blockly project which provides a more full-featured React component or hook for your application. The demo in samples is pretty bare-bones and you'd have to do a lot of React-related setup yourself, and the core team doesn't really have the React experience needed to help you debug any problems.
Maribeth