css-layout-patterns

name	css-layout-patterns
description	CSS and Tailwind v4 layout patterns. Use for @apply not working in SCSS, @reference tailwindcss, flex height chain, overflow not working, flex:1 in flex-row, page scrolling instead of container, dark theme styling, or flex layout debugging.
triggers	["@apply","@reference","Tailwind","SCSS","flex","overflow","scrolling","page scrolls","height chain","layout","dark theme","responsive","breakpoint","min-height","CSS"]
negative_triggers	["signal","effect","computed","Python","backend","test","spec","Karma","API"]

CSS & Layout Patterns

Theme

Facet uses a dark theme with Angular Material and Tailwind v4:

• Background: #0b0b0b (near-black)
• Primary: Material green palette
• Accent: Cyan highlights
• All components should assume dark background. Use light text colors, subtle borders (border-white/10), and translucent hover states (hover:bg-white/[0.08]).

Tailwind v4: @apply in SCSS (CRITICAL)

All component SCSS files using @apply MUST include @reference as the first line:

@reference "tailwindcss";

.my-class {
    @apply flex items-center gap-2;
}

Without @reference "tailwindcss";, @apply directives won't resolve in Tailwind v4.

Common Errors

• @apply silently ignored: No error, styles just don't apply -- always check for missing @reference
• Order matters: @reference must come BEFORE any @apply usage
• Per-file requirement: Each .scss file needs its own @reference, not just the root

Checking a Component

# Find SCSS files using @apply without @reference
grep -rn "@apply" client/src/ --include="*.scss" -l | xargs grep -L "@reference"

Tailwind-First Rule (CRITICAL)

Never create custom SCSS classes when a standard Tailwind utility exists:

Bad (custom SCSS)	Good (Tailwind)
.detail-section { margin-bottom: 24px }	mb-6
.clickable-row { cursor: pointer; &:hover { background: rgba(255,255,255,0.08) } }	cursor-pointer hover:bg-white/[0.08]
.text-center { text-align: center }	text-center
.full-width { width: 100% }	w-full
h3 { margin-bottom: 16px; font-weight: 500 }	mb-4 font-medium on <h3>

When touching a component's template/SCSS:

1. Check SCSS for custom classes replaceable by Tailwind
2. Flag hardcoded pixel values -- use Tailwind spacing (mb-4, p-2, gap-2)
3. Keep SCSS empty if all styling is achievable via Tailwind classes

Flex Height Chain Pattern

Problem: Page scrolls instead of container scrolling

Every element from viewport to scroll container must maintain the flex chain:

viewport -> html -> body -> app-root -> main -> content -> scroll-container

Each element needs:

display: flex;
flex-direction: column;
flex: 1;
min-height: 0; /* CRITICAL - allows flex children to shrink */
overflow: hidden; /* or auto on the scroll container */

flex-row vs flex-col Height Control

Parent Direction	Child Height Control	Why
flex-direction: column	flex: 1	Main axis is vertical -> flex controls height
flex-direction: row	height: 100%	Main axis is horizontal -> flex controls width only

Common mistake: flex: 1 in a flex-row parent does NOT constrain height!

Columns Don't Fill Width

Add width: 100% to elements in flex-row containers.

Finding Chain Breaks

Look for elements where clientHeight > parentHeight:

{ name: '.gallery-grid', height: 3200, parentHeight: 708, overflows: true }
//                        ^^^^         ^^^^                ^^^^^^^^^^^^
// This element needs height constraint

Tailwind Group-Scoped Hover

Use named groups to scope hover effects to specific areas (e.g., image-only overlay, not the entire card):

<!-- group/card wraps the whole card, group/img wraps just the image -->
<div class="group/card rounded-lg overflow-hidden">
  <div class="group/img relative">
    <img src="..." class="w-full" />
    <!-- This overlay only appears when hovering the image area -->
    <div class="absolute inset-0 bg-black/50 opacity-0 group-hover/img:opacity-100 transition-opacity">
      ...action buttons...
    </div>
  </div>
  <!-- Tags/details below — NOT affected by image hover -->
  <div class="p-2">tags, scores, etc.</div>
</div>

mat-icon Centering in Small Containers

mat-icon has default line-height that misaligns in small round buttons. Fix:

<!-- Container: use inline-flex, not flex -->
<button class="w-7 h-7 rounded-full inline-flex items-center justify-center">
  <!-- Icon: override size AND line-height -->
  <mat-icon class="!text-base !w-4 !h-4 !leading-4">star</mat-icon>
</button>

Common Mistake Reference

Symptom	Cause	Fix
Page scrolls instead of container	Missing height constraint in chain	Add flex: 1 or height: 100%
Content clipped unexpectedly	Missing min-height: 0	Add min-height: 0
flex: 1 doesn't constrain height	Parent is flex-row	Use height: 100% instead
Columns don't fill width	Missing width constraint	Add width: 100%
@apply doesn't work	Missing @reference	Add @reference "tailwindcss"; first line
Overflow not scrolling	Missing min-height: 0 on parent	Add to all flex ancestors
Dark theme text invisible	Using default dark text on dark bg	Use text-white or text-white/70

Diagnostic Script (Chrome DevTools MCP)

// Quick page-level check
() => {
  const body = document.body;
  const scrollContainer = document.querySelector('.scroll-container');
  return {
    viewport: { w: window.innerWidth, h: window.innerHeight },
    pageScrolls: body.scrollHeight > body.clientHeight,
    containerScrolls: scrollContainer ?
      scrollContainer.scrollHeight > scrollContainer.clientHeight : 'not found',
    issue: body.scrollHeight > body.clientHeight ?
      'Page scrolling - check flex height chain' : 'Container scrolling - OK'
  };
}

// Detailed chain trace -- find where chain breaks
() => {
  const selectors = ['app-root', 'main', '.content', '.gallery-grid', '.scroll-container'];
  return selectors.map(sel => {
    const el = document.querySelector(sel);
    if (!el) return { name: sel, error: 'not found' };
    const style = getComputedStyle(el);
    return {
      name: sel,
      height: el.clientHeight,
      parentHeight: el.parentElement?.clientHeight || 0,
      overflows: el.clientHeight > (el.parentElement?.clientHeight || 0),
      display: style.display,
      flexDirection: style.flexDirection,
      flex: style.flex,
      minHeight: style.minHeight,
      overflow: style.overflow
    };
  });
}

Debugging Steps

1. Run mcp__chrome-devtools__evaluate_script with the diagnostic script
2. Find which element breaks the chain (child height > parent height)
3. Check parent's flex-direction to determine fix:
   • Column parent -> add flex: 1; min-height: 0; to child
   • Row parent -> add height: 100%; min-height: 0; to child
4. Add overflow: hidden to containers, overflow-y: auto to scroll target
5. Verify at multiple breakpoints (mobile, tablet, desktop)

Responsive Testing Breakpoints

// Standard Tailwind v4 breakpoints
// sm: 640px, md: 768px, lg: 1024px, xl: 1280px, 2xl: 1536px

// Test at common sizes via Chrome DevTools MCP:
mcp__chrome-devtools__resize_page({ width: 1920, height: 1080 }); // Desktop
mcp__chrome-devtools__resize_page({ width: 1280, height: 800 });  // Laptop
mcp__chrome-devtools__resize_page({ width: 768, height: 1024 });  // Tablet
mcp__chrome-devtools__resize_page({ width: 375, height: 667 });   // Mobile

Examples

User says: "@apply isn't working in my component SCSS"

1. Check the SCSS file for @reference "tailwindcss"; as the first line
2. If missing, add it before any @apply usage
3. Verify each SCSS file has its own @reference (per-file requirement)

User says: "The page scrolls instead of just the gallery grid"

1. Run the flex height chain diagnostic script via Chrome DevTools MCP
2. Find the element where overflows: true -- that's where the chain breaks
3. Check parent's flex-direction: column -> add flex: 1; min-height: 0;; row -> add height: 100%; min-height: 0;
4. Add overflow-y: auto on the intended scroll container
5. Verify at desktop and mobile breakpoints

User says: "Should I use custom SCSS or Tailwind classes?"

1. Always prefer Tailwind utility classes over custom SCSS
2. Check if a standard Tailwind class exists for the desired style
3. Only write custom SCSS when Tailwind cannot express the pattern (e.g., complex selectors, ::ng-deep)