CSS Flexbox Generator
Build flex container and item properties visually, with a live preview and copy-ready CSS
.container {
display: flex;
flex-direction: row;
flex-wrap: nowrap;
justify-content: flex-start;
align-items: stretch;
gap: 12px;
}About this tool
The ToolNinja CSS Flexbox Generator builds flex container and item properties visually — direction, wrap, justify-content, align-items, align-content, and gap for the container, plus align-self and flex-grow for an individually selected item — with a live preview that updates instantly and copy-ready CSS below it. Flexbox's own terminology is a common source of confusion (justify-content vs align-items, which axis each one actually controls, what 'main axis' even means once you flip flex-direction to column), and most of that confusion only resolves by seeing it move. Dragging each control and watching the preview boxes react is faster than re-reading the spec for the tenth time. Everything runs 100% in your browser — the preview is live React/CSS, not a canvas rendering, so what you see matches real flexbox behavior exactly.
When to use it
- →Prototyping a navbar, card row, or button group's alignment before writing it in your actual stylesheet
- →Understanding how flex-direction: column flips which axis justify-content and align-items each control
- →Demonstrating align-self overriding a single item's alignment within an otherwise uniform row
- →Generating a starting flex-wrap + gap layout for a responsive component
Tips
- ◆Switching flex-direction to column swaps which axis justify-content and align-items each control — justify-content always controls the main axis, align-items the cross axis.
- ◆align-content only has a visible effect when flex-wrap isn't nowrap and there's more than one line to distribute — the tool hides it otherwise since it would do nothing.
- ◆gap works on flex containers in every current browser — there's no need for the old margin-based spacing hacks.
Frequently asked questions
What's the difference between justify-content and align-items?
justify-content controls alignment along the main axis (the direction flex-direction points — horizontal for row, vertical for column). align-items controls alignment along the cross axis (perpendicular to that). Flipping flex-direction swaps which one feels like 'horizontal' and which feels like 'vertical,' which is the single most common source of flexbox confusion.
When should I use CSS Grid instead of Flexbox?
Flexbox is one-dimensional — it's built for laying out a single row or column of items. Grid is two-dimensional — use it when you need to control rows and columns together, like a page layout or a card gallery with specific column spans. A lot of real UIs use both: Grid for the overall page structure, Flexbox for aligning items within one row of it.
Why isn't align-self doing anything on my selected item?
align-self only has an effect when the container's align-items value doesn't already stretch items to fill the cross axis in a way that leaves no room to move, or when the item has an explicit size smaller than the cross-axis space available. If the container is align-items: stretch and the item has no fixed height/width on the cross axis, it may visually fill the space regardless of align-self until you give it an explicit size.