Decision 0005 · accepted · 2026-10-18
Headers and the rail are 56px, with a square top-left corner
Headers are 56px high and the icons-only rail is 56px wide plus a 1px seam, so the top-left corner stays a 56px square.
Context
The product's brutal theme had 62px headers and a 64px rail, including a 2px border. Review found the rail too wide. The product's owner pinned a rule in code that the top-left cell, which holds the workspace, is always square, whatever else changes; a UI test (leftrail-square-slot) enforces it. The product's Elegant theme already used 56px for both.
Decision
The rail is 56px wide plus a 1px line-seam, and every header (rail, sidebar, panel, drawer, phone top bar row) is 56px high, so the top-left corner is a 56px square and the seams under the headers line up.
Consequences
Narrowing the rail means every header shrinks with it. The labeled rail needs 68px to fit names such as Computers, which makes its top-left corner 68×56 and breaks the square-corner test. Choosing it means changing that test, or making every header 68px high; see Open questions.