Problem

FloatingIndicator uses target.getBoundingClientRect() and parent.getBoundingClientRect() to compute dimensions and position offsets.

getBoundingClientRect() returns values in viewport coordinate space, which incorporates any CSS scale transforms (transform: scale(...)) applied to ancestor elements or during enter/exit animations (e.g. Modal transitions).

When inline CSS width, height, and transform values are assigned using these viewport-space measurements on an element inside a scaled ancestor:

• The ancestor's scale factor is applied a second time to the indicator.
• The floating indicator (and components using it internally, such as SegmentedControl) renders undersized (e.g., ~90% of the target's width) and shifted toward the transform origin.
• ResizeObserver does not correct the indicator after transition completion because CSS transforms do not alter unscaled content-box layout geometry.

Solution

Normalized viewport measurements back into the parent's local coordinate system in packages/@mantine/core/src/components/FloatingIndicator/use-floating-indicator.ts:

• Computed horizontal (scaleX) and vertical (scaleY) scale factors by comparing parent.getBoundingClientRect() against parent.offsetWidth and parent.offsetHeight.
• Guarded against zero dimensions (offsetWidth === 0 or offsetHeight === 0) to safely fallback to 1 when elements are hidden or unmounted.
• Normalized top, left, width, and height by dividing viewport-space deltas and dimensions by scaleY and scaleX.
• Added a new story ScaledAncestor to packages/@mantine/core/src/components/SegmentedControl/SegmentedControl.story.tsx to visually test indicator geometry under scaled ancestors.

Tests

• Automated Tests: Added a unit test in packages/@mantine/core/src/components/FloatingIndicator/FloatingIndicator.test.tsx asserting correct normalization when parent bounding geometry is scaled. Verified that all 316 @mantine/core Jest test suites (9,725 tests) pass (npm run jest @mantine/core).
• Build, Typecheck & Formatting: Successfully verified that the codebase typechecks (npm run typecheck), builds without errors (npm run build), passes linting (npx oxlint), and follows repository formatting (oxfmt).
• Manual Verification: Verified visually using the new ScaledAncestor story in Storybook (SegmentedControl > ScaledAncestor).

Resolves #9070