CSS Flexbox Generator

They control alignment along different axes. justify-content aligns flex items along the main axis — the direction your flex-direction is set to. So if flex-direction is row (the default), justify-content controls horizontal alignment (flex-start, center, flex-end, space-between, space-around, space-evenly). align-items controls the cross axis — perpendicular to the main axis. With flex-direction: row, align-items controls vertical alignment (flex-start, center, flex-end, stretch, baseline). The mental model that helps: 'justify-content distributes space, align-items controls cross-axis positioning'. If you ever switch flex-direction to column, the two axes flip — justify-content now controls vertical, align-items controls horizontal. The generator's live preview makes this immediately obvious because the layout reflows the moment you change direction.

Flexbox is for one-dimensional layouts — a row of buttons, a navigation bar, a stack of cards. Grid is for two-dimensional layouts where you need to control rows AND columns simultaneously, like a dashboard with a sidebar, header, main content, and footer. The simple rule of thumb: if you can describe the layout as 'a line of things' (horizontal or vertical), use Flexbox. If you need precise control over both axes — 'this card spans two columns and three rows' — use Grid. In practice modern layouts use both: Grid for the page-level skeleton, Flexbox for components inside each grid cell. Don't fall into the trap of using Flexbox for everything just because it's familiar; Grid is dramatically simpler for two-dimensional cases.

flex: 1 is shorthand for flex: 1 1 0%, which sets flex-grow: 1, flex-shrink: 1, flex-basis: 0%. In plain English: 'take an equal share of available space, shrink if needed, and start from a base size of zero'. It's the right answer for the common case of 'I want these three boxes to fill the row equally regardless of content'. If you instead write flex: 1 1 auto (which is also valid shorthand as flex: auto), each item starts at its content size and only the leftover space is divided up — which is what you want when you have items of different natural sizes that should stay roughly proportional. Knowing the difference between flex: 1 (equal sizes) and flex: auto (proportional) saves a lot of debugging time.

By default, flex items have flex-shrink: 1 and an implicit min-width: auto, which means they refuse to shrink smaller than their content. If you set width: 200px on a flex item containing a long word like 'antidisestablishmentarianism', the item will overflow rather than shrink, because the unbreakable word's content width acts as a floor. The fix is min-width: 0 on the flex item — this overrides the implicit minimum and lets the item shrink past its content size. This is the most common Flexbox gotcha and the answer to about half of 'why is my Flexbox layout broken' questions on Stack Overflow. The generator outputs working code, but if you adapt it for production with text content, remember to add min-width: 0 to children that contain long text.

Yes, in everything that matters in 2026. Flexbox has full support in Chrome, Edge, Firefox, Safari, and all mobile browsers going back many years. The only caveats are very old IE 10/11, which had a buggy older version of the spec — but those browsers have negligible market share now and most projects can ignore them. If you do need IE 11 support for some reason (legacy enterprise tools), stick to flex-direction, justify-content, align-items, and flex-grow/shrink/basis; avoid gap, which IE 11 doesn't support. For gap polyfill, fall back to negative margins on the container with positive margins on items — ugly but it works.