Bug 295801

Per spec (https://drafts.csswg.org/css-anchor-position-1/#default-scroll-shift) > After layout has been performed for abspos, it is additionally shifted by the default scroll shift, as if affected by a transform (before any other transforms). But currently, it seems we're applying the scroll compensation transform after other transforms: void RenderLayer::updateTransformFromStyle(TransformationMatrix& transform, const RenderStyle& style, OptionSet<RenderStyle::TransformOperationOption> options) const { auto referenceBoxRect = snapRectToDevicePixelsIfNeeded(renderer().transformReferenceBoxRect(style), renderer()); renderer().applyTransform(transform, style, referenceBoxRect, options); // https://drafts.csswg.org/css-anchor-position-1/#anchor-pos // "The positioned element is additionally visually shifted by its snapshotted scroll offset, as if by an additional translate() transform." if (m_snapshottedScrollOffsetForAnchorPositioning) transform.translate(m_snapshottedScrollOffsetForAnchorPositioning->width(), m_snapshottedScrollOffsetForAnchorPositioning->height()); makeMatrixRenderable(transform, canRender3DTransforms()); }