Why this matters
Flexbox is the foundation of modern CSS layout, yet the relationship between its properties is notoriously difficult to internalize from documentation alone. The interaction between `flex-direction`, `justify-content`, and `align-items` changes meaning depending on which axis is primary, and most developers learn Flexbox by trial and error in DevTools rather than from first principles. This iterative process works, but it is slow and does not build the mental model needed to write Flexbox CSS without a visual crutch.
This playground eliminates the guesswork by giving you direct control over every major Flexbox container property through dropdowns and a live preview with colored boxes. Changing `flex-direction` from `row` to `column` immediately shows how `justify-content` and `align-items` swap their visual roles. Adjusting `gap` and toggling `flex-wrap` reveals how items reflow, which is the kind of rapid feedback loop that turns confusion into intuition in minutes rather than hours.
Property reference table
| Property | Options | What it controls |
|---|---|---|
| flex-direction | row, row-reverse, column, column-reverse | Main axis direction |
| justify-content | flex-start, center, flex-end, space-between, space-around, space-evenly | Main axis distribution |
| align-items | stretch, flex-start, center, flex-end, baseline | Cross axis alignment |
| flex-wrap | nowrap, wrap, wrap-reverse | Wrapping behavior |
| gap | 0px–40px | Space between items |
| Items | 1–10 boxes | Number of children |
How to use it
Select a `flex-direction` value to set whether items flow horizontally (row) or vertically (column), including reversed variants.
Choose `justify-content` to distribute items along the main axis — use `space-between` for nav bars, `center` for hero sections, or `space-evenly` for card grids.
Set `align-items` to position items on the cross axis — `stretch` fills the container height, `center` vertically centers, and `baseline` aligns text baselines.
Toggle `flex-wrap` to allow items to flow onto new lines when they exceed the container width.
Adjust the `gap` slider to control spacing between items without adding margins to each child.
Add or remove preview items using the controls to see how the layout behaves with 1 to 10 children.
Click Copy to grab the generated container CSS and paste it directly into your stylesheet.
Testing your result
Set `flex-direction` to `row`, `justify-content` to `space-between`, and add three items. The first and last items should touch the container edges with the middle item centered between them. Switch `flex-direction` to `column` and confirm the same spacing pattern now applies vertically. Set `align-items` to `center` with `flex-direction: row` to verify all items are vertically centered within the container. Toggle `flex-wrap` to `wrap` with eight items and a narrow container to confirm items flow onto the next line. These checks validate that the generated CSS matches standard Flexbox behavior.
Common mistakes
Confusing `justify-content` (main axis) with `align-items` (cross axis) — the axes swap visually when you change `flex-direction`, which is the most common source of Flexbox confusion.
Expecting `align-items` to center vertically when `flex-direction` is `column` — in that case, `align-items` controls horizontal alignment and you need `justify-content: center` for vertical centering.
Using `space-evenly` without understanding it differs from `space-around` — `space-around` uses half-gaps at the edges while `space-evenly` uses full gaps everywhere.
Forgetting that this playground generates container-level CSS only — individual item properties like `flex-grow`, `align-self`, and `order` must be added to child elements in your own stylesheet.
Assuming vendor prefixes are needed — all modern browsers have supported unprefixed Flexbox since 2017.
Edge cases and options
The `baseline` value for `align-items` is particularly useful when child elements contain text of varying font sizes and you want their text baselines to align horizontally — think of a row of badges or a form with labels of different lengths. The `stretch` value makes items fill the cross-axis dimension by default, which means if you set a fixed height on the container and leave child heights unspecified, all children will stretch to match. The `wrap-reverse` option is rarely used but valuable for right-to-left or bottom-up layouts where items should fill from the bottom. The playground focuses on container properties because those define the layout structure; item-level overrides belong in your production CSS.
Real-world use cases
Frontend developers prototyping navbar, footer, and card layouts without switching between editor and browser.
Design system authors documenting Flexbox patterns with copy-paste-ready CSS snippets for their component libraries.
CSS learners building intuition for how justify-content and align-items interact across different flex-directions.
Responsive design workflows where the same container CSS is tested with different numbers of items to ensure graceful reflow.
Frequently asked questions
Q: What is the difference between justify-content and align-items?
A: justify-content positions items along the main axis (the direction flex-direction points). align-items positions them along the cross axis (perpendicular to the main axis). Together they give you full 2D control over item placement.
Q: When should I use flex-wrap?
A: Whenever you have a variable number of items that should reflow on smaller screens — tag clouds, chip rows, and photo galleries. Use wrap-reverse for bottom-up layouts.
Q: Why is space-evenly different from space-around?
A: space-around adds half-gaps at the edges, so items have equal space around each one but less at the container edges. space-evenly adds full gaps everywhere, including at the edges, for a more balanced look.
Q: How does align-items: baseline work?
A: It aligns items along their text baseline, which is useful when items have different font sizes and you want their text to line up — like a row of mixed-size badges.
Q: Can I control individual items from this playground?
A: The playground focuses on container properties. To control individual items, add flex: 1, align-self, order, or flex-grow to the child elements in your own stylesheet.
Q: Is the output CSS prefix-free?
A: Yes. Flexbox has been unprefixed in all modern browsers since 2017. The output works as-is on Chrome, Safari, Firefox, and Edge.
Start using it now
Try the Flexbox Playground tool. See also CSS Grid Generator, Media Query Generator, and Gradient Generator.
