AI coding agents struggle with CSS. Asked to move a sidebar 10px, an agent edits a margin, then an order, then a flex-basis, and something else moves. It then reports the change as done while the page is broken. Flex and grid have no single "left" property, so the agent has to guess which one to touch. QSS makes layout addressable. Every structural value is an explicit, single-purpose quantity on a 1000-unit canvas grid (1 qnt = canvas width / 1000, computed in pure CSS), so each edit has one target and the same numbers hold at any screen size. Frames sit flat on one canvas, isolate their layout, and overlays portal to the document root. QSS also audits what can be checked statically. Two auditors flag violations such as !important, inline layout styles, undeclared sizes and raw viewport units. RED marks a rule violation and ORANGE a judgment call. Static checks can't prove a page renders, so QSS includes a render check for the compiled CSS alone, and its design history is explicit that only a real browser is real proof. QSS was extracted from a Rails development tool, which was its first consumer. Its early custom parser was a bug farm, and an invented syntax costs agents more than it buys. Structure moved to plain CSS custom properties; bracket values remain for content such as spacing and sizes. What was tried and dropped is in docs/DESIGN_HISTORY.md. Status: 0.x. Expect names and APIs to change before 1.0.