When short stacks of code are triggered, green flag can appear to flicker

[benjiwheeler]

Expected Behavior

Unclear what's expected behavior; but when you press buttons or otherwise provide input to a Scratch program, you should expect the green flag's active/highlighted state to be active when the project is handling input, and non-active when the project is not running. It should not be distracting.

Actual Behavior

When hat blocks are attached to stacks of code that execute quickly, input can appear to cause the green flag and stop icon to flicker:

Steps to Reproduce

View the project https://scratch.mit.edu/projects/320489108/ , or create your own:

1. attach a "When right arrow key pressed" block to a "change x by 10" block.
2. repeatedly press the right arrow.

Related issues

• green flag icon render performance: Figure out hover/active states for icon buttons #4382
• green flag incorrectly appearing to be active: Edge-triggered(?) hat blocks make the green flag always look active scratch-vm#1948

Solutions

@paulkaplan suggested we might obtain behavior more like Scratch 2.0 (where the transitions followed the same pattern, but were visibly longer and thus looked less glitchy) by merely tinkering with the flag/stop icons' css transition settings.