Core behavior and first-principles view

Qt style sheets can create coherent visual systems, but maintainability depends on selector discipline and accessible state design. Styling should support function, not just decoration.

Selector scope and specificity determine which widgets actually receive intended styles.

State styles (hover, focus, disabled) are usability signals, not optional extras.

Theme consistency requires tokenized color and spacing strategy rather than random overrides.

Low-level model and equations

WCAG contrast ratio reference:

Where:

• $L_1$: lighter luminance
• $L_2$: darker luminance

How to build this correctly in practice

1. Define a small palette/token map first, then apply across components.
2. Keep style modules segmented by widget family or feature area.
3. Test styles in focused, hovered, disabled, and error states.
4. Track style regressions with visual snapshots for critical screens.

Common failure patterns and review checks

• Overly specific selectors make refactors brittle.
• Removing focus cues harms keyboard accessibility immediately.
• Large monolithic style files are difficult to reason about.
• Cross-platform style assumptions should be verified on target OS set.

A reliable style system is one you can evolve without breaking usability or introducing hidden selector conflicts.