Modern UI workbench styling feels visually noisy and less usable

The experimental `Workbench > Experimental: Modern UI` setting currently changes the workbench so side bars and the bottom panel appear as floating cards with rounded corners, gaps, and refreshed styling.

I find this visual direction substantially worse than the current workbench UI. The floating-card treatment makes the editor feel more cluttered and less integrated, especially for dense development workflows where panels, side bars, and editor groups are used continuously. The extra gaps and rounded container boundaries draw attention to the chrome instead of the code and make the workspace feel visually fragmented.

Please consider either:

- preserving a stable, clearly supported option to keep the current workbench UI, or
- revisiting the Modern UI treatment before making it the default, with particular attention to reducing gaps, visual fragmentation, and card-like panel styling.

This is subjective visual feedback, but the proposed default-value change makes it important for users who prefer the existing workbench density and structure to have a durable way to opt out.

Thank you