a joined group's segments each drew their own 1px top/bottom border in the same token as the group's own, and the two lines landed adjacent rather than overlapping, so the selected tab read as a 2px edge with the ::before inset shadow stacking a third band under it. the -my-px meant to pull them together never applied: items-center left the segments at their natural height instead of stretching, so the margins only shrank the flex line the group had already outgrown. follows the appview's .btn-group instead — the group is the only thing drawing a horizontal border, its segments take border-y-0 and stretch to fill the inner box. the x seams are unchanged, still one divider each via -ml-px. the recessed surface also needed dark:bg-background-canvas: subtle sits below default in light (#f9fafb vs #fff) but above it in dark (#374151 vs #1f2937), so an unselected segment came out lighter than the selected one. canvas (#111827) is the appview's gray-900. Signed-off-by: eti <eti@eti.tf>