grid-layout-systems

name	grid-layout-systems
description	Use when laying out a page or component, choosing between CSS Grid and Flexbox, setting up a column grid, aligning nested components to a parent grid, or building responsive card/dashboard layouts.
metadata	{"references":["references/grid-patterns.md","references/responsive-strategies.md","references/spacing-systems.md"]}

Grid Layout Systems

Choose the Right Tool

Need	Use
2D page layout (rows + columns)	CSS Grid
1D component layout (row OR column)	Flexbox
Nested element aligned to parent grid	grid-template-columns: subgrid
Auto-reflowing card grid (no breakpoints)	Grid + auto-fit minmax()
Component responsive to container, not viewport	Container queries

Workflow

1. Decide page-level vs component-level. Page → Grid. Component → Flexbox.
2. Pick a column count: 12 (flexible), 8 (simpler), 4 (mobile).
3. Set tokens for --gap, --max-width, spacing scale (see Spacing).
4. Build layout with named areas OR repeat(N, 1fr).
5. Add responsive behavior: prefer auto-fit minmax() over breakpoints; fall back to @media (min-width: ...) for structural changes.
6. Validate against the checklist at the bottom.

12-Column Grid (copy-paste)

.container {
  display: grid;
  grid-template-columns: repeat(12, 1fr);
  gap: 24px;
  max-width: 1200px;
  margin: 0 auto;
  padding: 0 24px;
}

.content { grid-column: span 8; }
.sidebar { grid-column: span 4; }
.hero    { grid-column: 1 / -1; }
.narrow  { grid-column: 3 / 11; }

Named Grid Areas (Holy Grail)

.page {
  display: grid;
  grid-template-columns: 240px 1fr 300px;
  grid-template-rows: auto 1fr auto;
  grid-template-areas:
    "header header header"
    "nav    main   aside"
    "footer footer footer";
  min-height: 100vh;
}
.header { grid-area: header; }
.nav    { grid-area: nav; }
.main   { grid-area: main; }
.aside  { grid-area: aside; }
.footer { grid-area: footer; }

Auto-Reflow Card Grid

/* auto-fit: empty tracks collapse; auto-fill: empty tracks preserved */
.card-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(min(280px, 100%), 1fr));
  gap: 24px;
}

Subgrid (align nested to parent)

.page { display: grid; grid-template-columns: repeat(12, 1fr); gap: 24px; }
.card-group {
  grid-column: 1 / -1;
  display: grid;
  grid-template-columns: subgrid;
}
.card { grid-column: span 4; }

Flexbox Patterns

/* Navbar */
.navbar { display: flex; align-items: center; justify-content: space-between; }

/* Card with footer pinned to bottom */
.card { display: flex; flex-direction: column; height: 100%; }
.card-body { flex: 1; }
.card-footer { margin-top: auto; }

/* Centering */
.center { display: grid; place-items: center; }

Container Queries

.card-container { container-type: inline-size; container-name: card; }

@container card (min-width: 400px) {
  .card { display: grid; grid-template-columns: 120px 1fr; gap: 16px; }
}
@container card (max-width: 399px) {
  .card { display: flex; flex-direction: column; }
}

Spacing Tokens (Base-4)

:root {
  --space-1: 4px;  --space-2: 8px;   --space-3: 12px;  --space-4: 16px;
  --space-6: 24px; --space-8: 32px;  --space-12: 48px; --space-16: 64px;
}

• Intra-component: 4–12px. Inter-component: 16–24px. Section: 32–96px.

Validation Checklist

• DevTools grid overlay shows all major elements aligned to the same column tracks.
• No element uses absolute positioning to escape the grid.
• Resize from 320px → 1920px: no horizontal scroll, no overlaps, no orphaned items.
• Cards in an auto-fit grid reflow without breakpoints.
• Sub-components in nested grids align to the parent (use subgrid or matching tracks).
• Gap values come from spacing tokens, not magic numbers.

Deep Dive References

• Grid Patterns — Holy Grail, dashboard, magazine, masonry, sidebar, sticky footer
• Responsive Strategies — Mobile-first, content-driven breakpoints, fluid grids
• Spacing Systems — Base units, hierarchy, density modes, token naming

Next Steps

• Typography Systems: Align type to baseline grid
• Responsive Design: Broader responsive strategy
• CSS Architecture: Organize grid utilities
• Design Tokens: Encode spacing and breakpoints as tokens