Chapter 6: Layout Engines: Flexbox, Grid, and Normal Flow

How browsers position elements, and when to use Flexbox, Grid, or just let it flow

As a front-end developer, mastering layout is one of the most valuable things you can do.

And I don’t mean memorizing Flexbox utilities or copy-pasting Grid templates. I mean truly understanding how the browser lays things out, what tools it offers, and how to choose the right one for what you’re building.

This chapter walks you through:

• The difference between flow, Flexbox, and Grid
• When to use what (and when not to)
• Real examples, debugging tips, and layout gotchas

Section 6.1: Normal Flow, The Browser’s Default

Before CSS layout systems evolved, we had normal flow and honestly, it’s still a solid foundation.

In Normal Flow:

• Block elements stack vertically, taking up the full width of their parent
• Inline elements flow horizontally, wrapping when needed

<div>
  <p>This is a block</p>
  <span>This is inline</span>
</div>

Pros:

• Simple, predictable
• Perfect for text content and long-form documents

Limitations:

• No control over alignment
• Can’t place things side by side without floating or hacking

Use normal flow for:

• Text-heavy content
• Long articles
• Default layouts before enhancement

Section 6.2: Flexbox: One Axis to Rule Them All

Flexbox is a one-dimensional layout system. You pick either a row or a column to control.

.container {
  display: flex;
}

Main axis vs cross axis:

• flex-direction: row → main axis is horizontal
• flex-direction: column → main axis is vertical

Use justify-content to control alignment along the main axis
Use align-items for the cross axis

Common properties:

display: flex;
flex-direction: row;
justify-content: space-between;
align-items: center;
gap: 1rem;

For children:

• flex-grow: allow to expand
• flex-shrink: allow to shrink
• flex-basis: default size
• flex: shorthand for all three

Best use cases:

• Navbars
• Cards in a row
• Sidebar + content split
• Vertical centering

Flexbox makes a lot of old layout hacks (like floating divs) obsolete.

Section 6.3: Grid: When You Care About Structure

Grid is two-dimensional: it gives you full control over rows and columns.

.container {
  display: grid;
  grid-template-columns: 1fr 1fr 1fr;
  gap: 1rem;
}

Each 1fr means “take equal part of the available space”.

You can mix fixed and flexible units:

grid-template-columns: 200px 1fr;

Now column 1 is fixed, column 2 fills the rest.

Powerful grid features:

• grid-template-areas: name your layout
• grid-auto-flow: row vs column direction
• auto-fit and auto-fill: responsive layout magic

grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));

This builds a responsive grid that wraps automatically.

Section 6.4: Which Layout Tool Should You Use?

The core rule:

• Flexbox is for distribution along one axis
• Grid is for full-blown layout with rows + columns
• Normal flow is the fallback, useful until layout is needed

You can (and should) mix them.

Section 6.5: Nesting Flex and Grid

Example:

.main-layout {
  display: grid;
  grid-template-columns: 250px 1fr;
  height: 100vh;
}

.sidebar {
  background: #f4f4f4;
}

.content {
  display: flex;
  flex-direction: column;
  gap: 1rem;
}

Here, Grid lays out the overall page. Flexbox controls content spacing inside.

This is a common real-world combo.

Section 6.6: Responsive Techniques

Grid with auto-fit:

grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));

Items fill space and wrap automatically.

Flexbox with wrapping:

display: flex;
flex-wrap: wrap;
gap: 1rem;

Each item should have a defined width or flex-basis.

Use media queries or container queries to adjust breakpoints.

Section 6.7: Debugging Layout with DevTools

• Right-click → Inspect
• In Chrome or Firefox, enable Grid or Flex overlays
• Chrome DevTools shows:
  • Flex direction arrows
  • Item alignment
  • Gaps and track sizes

Bonus: Firefox has even better Grid inspection tools

Section 6.8: Common Layout Pitfalls

• Using Flexbox to fake a grid → use grid instead
• Forgetting to use gap → don’t space with margin
• flex: 1 doesn’t mean “fill all space” unless other items allow it
• Nested display: flex for everything → hurts readability
• Relying too much on media queries → try auto-fit first

Summary

• Normal flow is still useful for content, don’t overengineer
• Flexbox is perfect for rows or columns especially when you don’t need track-based layout
• Grid is best for full-page structures, cards, dashboards, and any 2D layout
• Combine layout models wisely
• Use DevTools to inspect, always debug visually

Resources

• MDN Web Docs: Flexbox
• MDN Web Docs: Grid
• CSS Tricks: A Complete Guide to Flexbox
• CSS Tricks: A Complete Guide to Grid

Coming Up Next

In Chapter 7, we’ll cover modern CSS selectors like :is(), :has(), :focus-visible, and :where() and how they let you write smarter, more accessible, and more maintainable CSS.