Free CSS Flexbox Generator - Build Flex Layouts Visually

justify-content controls alignment along the main axis (direction flex items flow). For flex-direction: row (default), main axis is horizontal - justify-content aligns items left-to-right. For flex-direction: column, main axis is vertical - justify-content aligns items top-to-bottom. align-items controls alignment along the cross axis (perpendicular to main axis). For row direction, cross axis is vertical - align-items aligns items vertically. For column direction, cross axis is horizontal. Mnemonic: justify = direction you are reading/moving, align = perpendicular. Common: justify-content: center; align-items: center; centers items both axes.

flex-basis sets initial size of flex item before growing/shrinking (like width but respects flex direction). Default: auto (uses element's content size). flex-grow controls how much item grows to fill available space (proportion). flex-grow: 1 = take equal share, flex-grow: 2 takes 2x more than flex-grow: 1 items. Default: 0 (no grow). flex-shrink controls how much item shrinks when container is too small. Default: 1 (items shrink equally). Shorthand: flex: grow shrink basis. Examples: flex: 1 = flex: 1 1 0% (grow, shrink, start from zero), flex: 0 0 200px = fixed 200px width (no grow/shrink).

Use Flexbox for: one-dimensional layouts (row OR column, not both), content-first layouts where size depends on content, navigation bars, simple card rows, aligning items within containers, components that need to wrap (flex-wrap). Use CSS Grid for: two-dimensional layouts (rows AND columns simultaneously), layout-first designs with fixed structure, complex page layouts, magazine-style designs, when you need items to align both horizontally and vertically across rows/columns. Rule of thumb: Flexbox for components, Grid for page layouts. Modern approach: use both together - Grid for overall page structure, Flexbox for component internals.

Flexbox does this automatically when align-items: stretch (default) is applied. All flex items in a row stretch to match tallest item's height. No extra CSS needed. If items don't stretch: check if items have explicit height set (remove it), ensure parent has display: flex, verify align-items is not set to flex-start/flex-end. For nested content to fill item height: make flex items into flex containers themselves (display: flex; flex-direction: column) and use flex-grow on children. Common use: pricing cards with different content amounts but same height. This is flexbox's killer feature - no JavaScript height matching needed.

By default, flex-shrink: 1 allows items to shrink below their content size when container is small. This can cause text overflow, truncation, or squished content. Fix: set flex-shrink: 0 on items that should not shrink below their content size, set min-width: 0 (resets default min-width: auto that prevents shrinking), use flex-wrap: wrap to let items wrap to next line instead of shrinking, set explicit min-width on items (e.g., min-width: 200px). For images: object-fit: cover or contain. Test layouts at narrow widths - overflow issues appear at mobile sizes. Modern approach: flex-wrap: wrap for responsive content.

gap property (formerly grid-gap, now works in Flexbox too) adds space between flex items without margins. Syntax: gap: 20px (uniform), gap: 20px 10px (row-gap column-gap). Benefits over margin: only between items (no extra space at edges), single property controls all spacing, changes with flex-direction automatically, no :last-child margin hacks. Browser support: modern browsers (2021+), use margin fallback for older browsers. Polyfill: @supports (gap: 1px) { / * use gap * / } @supports not (gap: 1px) { / * fallback margins * / }. gap is now standard spacing method for Flexbox and Grid. Use gap for internal component spacing, margin for external component spacing.