Container Width System

Give pages a few defined widths instead of a different max-width on every screen.

moderate Design Systems

What it adds

A small set of named page widths — narrow, standard, wide, and full-bleed — applied consistently across the app.

What your agent is told to do

1
Measure the max-width used on every top-level page and group them. Settings forms, prose, dashboards, and data tables usually want three or four distinct widths between them, not the eleven the codebase currently has.
2
Pick each width from the content it holds. A reading column is bounded by comfortable line length, a settings form by field width, and a table by the number of columns that must stay visible.
3
Make horizontal page padding part of the container rather than something each page adds, so content never touches the viewport edge on a narrow screen even at the widest setting.
4
Give full-bleed sections a defined way to escape the container and return, so a hero band or a full-width table can span the viewport while the text above and below stays aligned to the same column.
5
Do not force data-heavy screens into the reading width. Wide tables, canvases, and dashboards need the viewport, and constraining them to a prose column trades a real workflow for a typographic preference.

Edge cases it handles

Horizontal padding must survive at every width. A container that only sets max-width will let text run into the screen edge on small viewports, where the constraint is padding rather than the maximum.
Some sections legitimately need to break out — full-bleed images, sticky table headers, edge-to-edge banners — so there must be a supported escape rather than each page reaching for negative margins.
Modals, drawers, and side panels need widths drawn from the same set, or a dialog containing the same form as a page will render it at a different measure and look like a different product.
Article and documentation screens should stay narrow while data screens go wide, and a single global maximum cannot serve both, so the width belongs to the page rather than to the layout shell.
Nested containers silently compound their padding, so a container placed inside another must detect that and contribute nothing rather than doubling the inset.
Breakpoint values used to switch between widths come from Breakpoint Token System, and column counts and gutters inside a container come from Responsive Grid Tokens; this feature owns the outer boundary only.
A width expressed only in pixels will not respond to the user's root font size, which matters on screens that are mostly text.

Definition of done

The app defines no more than five named page widths and every page uses one of them.
No page declares its own max-width outside the system.
Content keeps its horizontal padding at every viewport size and never touches the screen edge.
There is a supported full-bleed escape that returns to the same alignment afterwards.
Modals, drawers, and panels draw their widths from the same set as pages.
Data-heavy screens are not constrained to the reading width.
Nested containers do not double their padding.
The feature matches the existing design system.
No existing functionality is broken.

Related features

Z-Index Registry

Spacing Scale

Shadow Scale

How it works

1

Copy the link

Grab the Markdown instruction URL for this feature.
2

Give it to your AI

Paste it into Claude Code, Cursor, v0, Lovable — whatever you build with.
3

It inspects, then implements

Your agent reads your existing app first, then adds the feature to fit it.

Works with your stack

These instructions are written to adapt. They tell the agent to detect your framework, match your existing design system, and reuse what you already have — rather than assuming a particular stack.

Need it tighter than that? Customize the feature and tell it exactly what you're running.