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Classic centering recipe: display:flex; justify-content:center; align-items:center; — works for any box, any screen size.
Flexbox is the CSS layout module designed for one-dimensional arrangements — rows or columns of items that need to align, distribute space, and adapt to different screen sizes. Before flexbox, centering a box both horizontally and vertically required fragile hacks with tables, absolute positioning, or mysterious margin tricks. With flexbox, that classic centering recipe is just three declarations: display:flex; justify-content:center; align-items:center. It is no exaggeration to say flexbox changed how the entire web is laid out.
The model is simple: you declare display:flex on a container, and its direct children become flex items that the container positions according to a handful of properties. The container controls the flow direction, how items distribute along the main axis, how they align on the cross axis, whether they wrap, and the gaps between them. Individual children can grow, shrink, and reorder themselves. Our free Flexbox Generator turns all of these properties into dropdowns and sliders with a live preview of three boxes, so you can build the exact layout you want visually and copy the resulting CSS.
Everything starts with display:flex on the container. Then flex-direction sets the main axis: row lays items out left to right, row-reverse flips them right to left, column stacks them top to bottom, and column-reverse stacks them bottom to top. The reverse values are handy for alternating layouts or right-to-left designs without touching your HTML order.
Next, justify-content distributes items along the main axis and offers six values: flex-start packs items at the beginning, flex-end packs them at the end, center groups them in the middle, space-between pushes the first and last items to the edges with even gaps between, space-around gives each item equal space on both sides, and space-evenly distributes all space — including at the edges — perfectly evenly. Then align-items controls the cross axis with five values: stretch (the default, making items fill the container's cross size), flex-start, flex-end, center, and baseline, which aligns items by their text baselines — ideal for lining up labels of different font sizes.
Two more properties complete the container toolkit. Flex-wrap decides what happens when items overflow: nowrap squeezes them onto one line, wrap lets them flow onto multiple lines, and wrap-reverse stacks the extra lines in the opposite direction. The gap property sets clean, consistent spacing between items — and between rows when wrapping — without the margin hacks that used to collapse or double up at container edges. Children get their own star property: flex-grow lets an item absorb leftover space, so setting flex-grow:1 on one child makes it expand to fill whatever room remains.
The control panel exposes every property described above as a dropdown or slider: direction, justify-content, align-items, wrap, gap, and per-item flex-grow. Below the panel, a live preview area shows three colored boxes rearranging themselves the instant you change anything. There is no faster way to develop an intuition for how space-between differs from space-around, or what baseline alignment actually does — you see it happen in real time.
When the preview matches the layout in your head, copy the generated CSS. The output is clean, commented, production-ready code covering both the container rules and the child rules. Paste it into your stylesheet and you are done. Use it to prototype navbars, card grids, form rows, footers, and hero sections in seconds instead of wrestling with the spec from memory. And once your layout is solid, polish it further: add depth with our Box-Shadow Generator, paint backgrounds with our CSS Gradient Generator, or style the calls to action with our CSS Button Generator.
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Flexbox handles one dimension brilliantly — a row or a column. When you need true two-dimensional control, with items aligned in both rows and columns simultaneously, CSS Grid is the right tool. A practical rule: use flexbox for components (navbars, button groups, form rows, media objects) and grid for page-level scaffolding (overall page regions, complex card matrices). They compose beautifully — a grid cell can itself be a flex container. Mastering flexbox first, with this generator as your playground, gives you the intuition that makes grid click faster later.
The classic beginner trap is forgetting that flex properties apply to the container, not the items — justify-content on a child does nothing. Another is expecting gap to work in very old browsers; it is universally supported in all modern browsers, but if you must support legacy ones, fall back to margins. Watch out for flex-shrink too: the default lets items shrink below their content size, which can squash images — set flex-shrink:0 or a min-width on items that must keep their size. Finally, remember that absolutely positioned children are removed from the flex flow entirely, so mixing the two needs deliberate planning. Build each pattern in the generator first, and these surprises disappear before they reach your production code.
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Justify-content distributes items along the main axis (set by flex-direction), while align-items aligns them along the cross axis. In a row layout, justify-content is horizontal and align-items is vertical; in a column layout, they swap.
Give the parent display:flex, justify-content:center, and align-items:center. That is the entire recipe — it centers the child both horizontally and vertically.
Yes. Flexbox is supported in every modern browser without prefixes. The gap property in flex containers is likewise supported everywhere modern, which the generator's output relies on.
Whenever one item should absorb leftover space — a search input expanding between a logo and a button, or main content filling the area beside a fixed sidebar. A value of 1 on one child (0 on the others) is the most common pattern.
Yes, the order property on flex items controls visual order independently of source order. Use it for responsive rearrangements, but keep the HTML order logical for screen readers and keyboard navigation.
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