CSS Flexbox Generator: Build Layouts Visually, Copy the CSS
Flexbox has enough interacting properties — direction, main-axis alignment, cross-axis alignment, wrapping — that getting a layout exactly right often means trial and error in dev tools. This generator lets you adjust every flex container property with a live visual preview, so you can see the result before copying a single line of CSS.
justify-content aligns along the main axis, align-items along the cross axis.
Main Axis vs. Cross Axis
Flexbox's mental model rotates with flex-direction: in row mode, the main axis is horizontal and the cross axis is vertical; in column mode, it's flipped. justify-content always controls the main axis and align-items always controls the cross axis — which is why the same align-items: center can look like vertical or horizontal centering depending on direction.
Why Wrapping Changes What's Available
flex-wrap: nowrap forces all items onto a single line (shrinking them if needed), so there's only one 'line' for align-items to position. Switching to wrap allows multiple lines, at which point align-content becomes relevant — it controls how those multiple lines are distributed within the container, independent of how items are positioned within each line.
gap Replaced a Lot of Margin Hacks
Before gap had broad support, spacing flex items required margins on individual children, which meant extra logic to avoid unwanted space on the first/last item's outer edge. gap on the container handles spacing between items only, cleanly, with no edge-case workarounds needed.
Practical Examples
A Horizontal Navbar
Items spread across the full width.
- 1.flex-direction: row
- 2.justify-content: space-between
- 3.align-items: center
A Centered Card Stack
Vertically stacked, centered content.
- 1.flex-direction: column
- 2.align-items: center
- 3.gap: 16px
Properties This Generator Covers
- flex-direction: row, row-reverse, column, column-reverse
- justify-content: main-axis alignment
- align-items: cross-axis alignment
- flex-wrap: single vs. multi-line
- align-content: multi-line distribution
- gap: spacing between items
Good Use Cases
- Prototyping a navbar, toolbar, or button group layout
- Learning how justify-content and align-items interact
- Quickly testing wrap behavior with a variable item count
- Generating a starting point to refine in your actual codebase
Frequently Asked Questions
What's the difference between justify-content and align-items?
justify-content controls alignment along the main axis (horizontal for flex-direction: row, vertical for column). align-items controls alignment along the cross axis, perpendicular to the main axis.
Why does align-content only show up when flex-wrap isn't nowrap?
align-content controls spacing between multiple lines of flex items when wrapping creates more than one row/column. With nowrap (the default, single line), there's only one line, so align-content has no visible effect.
What does flex-direction: row-reverse actually change?
It reverses the visual order of items along the main axis without changing their order in the underlying HTML/DOM — useful for RTL-style layouts or specific visual ordering without restructuring markup.
Should I use gap or margins to space flex items?
gap is the modern, simpler approach — it adds consistent spacing between items without the 'extra space on the outer edge' problem that margins on individual items create, and it's supported in all current browsers.
What's the difference between space-between, space-around, and space-evenly?
space-between puts all extra space between items (none at the edges). space-around gives each item equal space on both sides (so gaps between items look like 2x the edge gaps). space-evenly makes every gap — including edges — exactly equal.
Does this generator apply flex properties to the child items too?
No — it generates the container's flex properties (display: flex and its layout controls). Individual item properties like flex-grow, flex-shrink, or align-self would need to be added separately per item based on your specific layout needs.