CSS Flexbox Generator

What Is the CSS Flexbox Generator?

The CSS Flexbox Generator is a visual layout tool that lets you configure a flex container by clicking options rather than memorizing property names and values. Adjust flex-direction, justify-content, align-items, flex-wrap, align-content, and gap interactively, see the result immediately in the live preview, then copy the ready-to-paste CSS with one click. Everything runs in your browser — no account, no uploads, and the CSS is generated locally without sending anything to a server.

How to Use the Flexbox Generator

1. Set the flex-direction. Choose row to lay items horizontally (the default) or column to stack them vertically. The -reverse variants reverse the order of items.
2. Pick a justify-content value. This distributes space along the main axis. space-between gives equal gaps between items with no gap at the edges; space-evenly gives equal gaps including at the edges.
3. Pick an align-items value. This aligns items on the cross axis. stretch (the default) makes items fill the container height; center vertically centers them.
4. Enable flex-wrap if needed. Switch to wrap to let items flow onto new lines. The align-content option appears when wrapping is on, controlling how the rows themselves are distributed.
5. Set a gap. Type a value like 16px or 1rem to add uniform spacing between items. Clear the gap field to reveal separate row-gap and column-gap inputs.
6. Adjust item count. Drag the slider to add or remove preview boxes and see how the layout responds.
7. Copy the CSS. Click Copy CSS and paste the generated code directly into your stylesheet.

Understanding the Main Flexbox Properties

flex-direction

flex-direction defines the main axis of the flex container, which determines which direction items flow. The default is row, which places items left-to-right in left-to-right languages. column stacks items top-to-bottom. The -reverse variants swap the start and end points: row-reverse places items right-to-left and column-reverse places them bottom-to-top. This also switches which side flex-start and flex-end refer to for other properties.

justify-content

justify-content distributes free space along the main axis after all items and gaps are placed. The six values each produce a different spacing pattern:

• flex-start — items pack toward the start of the main axis (left in a row).
• flex-end — items pack toward the end of the main axis (right in a row).
• center — items cluster in the middle of the main axis.
• space-between — equal gaps between adjacent items; no gap at the start or end.
• space-around — each item gets equal space on both sides; edge items have half the gap of adjacent items.
• space-evenly — equal gaps between all items and at the start and end edges.

align-items

align-items controls how items sit on the cross axis within their line. stretch makes items expand to fill the container height (the default). flex-start aligns items to the top of the row; flex-end to the bottom; center vertically centers them. baseline aligns items so their text baselines line up — useful when mixing different font sizes or padding amounts.

flex-wrap and align-content

With flex-wrap: wrap, items that cannot fit on a single line break onto new lines. align-content then controls how those lines are distributed within the container. It only has a visible effect when there are multiple lines — if all items fit on one line, align-content does nothing. Think of align-content as the multi-line equivalent of justify-content: it distributes space between rows rather than between individual items.

Real-World Flexbox Layout Examples

Example 1: Navigation Bar

A typical navigation bar has a logo on the left and links on the right. The classic approach uses flexbox with justify-content: space-between on the container:

.navbar {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 16px;
}

The logo element takes up as much space as it needs, and the remaining space is pushed to the right, pressing the nav links against the right edge. Adding align-items: center ensures the logo and links are vertically centered in the bar regardless of their individual heights.

Example 2: Centering a Modal

Centering a modal or card perfectly in the viewport is a two-line pattern that trips up many developers who still reach for margin: auto with position: absolute:

.overlay {
  display: flex;
  justify-content: center;
  align-items: center;
  min-height: 100vh;
}

The overlay covers the full viewport height, and flexbox automatically centers the modal child element in both dimensions. No calculations, no negative margins, no top: 50%; transform: translate(-50%, -50%).

Example 3: Responsive Card Grid

A simple responsive card row that wraps to fewer columns on narrow screens:

.card-grid {
  display: flex;
  flex-wrap: wrap;
  gap: 24px;
}

.card {
  flex: 1 1 280px; /* grow, shrink, min-width */
  max-width: 400px;
}

Each card has a minimum width of 280px. If the container is wide enough for three cards, three appear per row. As the viewport narrows, cards wrap to fewer per row, and at small screen sizes each card takes the full width. This pattern eliminates the need for media query breakpoints in most cases.

Flexbox vs CSS Grid: Which Should You Use?

The most common question once you learn flexbox is when to switch to CSS Grid. The short answer: flexbox is one-dimensional, Grid is two-dimensional.

Use flexbox when your layout flows in one direction: a row of buttons, a column of form fields, a horizontal navigation. Flexbox excels at distributing space among items that vary in size and letting them grow or shrink to fill available room.

Use CSS Grid when you need explicit rows and columns simultaneously: a magazine-style page layout, a photo gallery with fixed grid lines, or a dashboard with named areas. Grid gives you precise control over placement in both dimensions.

In practice, most UIs combine both. A Grid might define the overall page structure (header, sidebar, main, footer), while Flexbox arranges the items inside each section. They compose naturally because flex items can themselves be grid containers and vice versa.

Common Flexbox Mistakes and How to Fix Them

Mistake 1: Putting flex properties on children instead of the parent

justify-content and align-items belong on the flex container (the element with display: flex), not on the flex items. Properties that go on children are flex-grow, flex-shrink, flex-basis, align-self, and order.

Mistake 2: Using margin to add gaps (pre-gap era habit)

Before the gap property was widely supported, developers used margin on items and then negated the edge margins on the container. The gap property is now supported in all modern browsers and is far simpler — it only applies spacing between items, never on the outer edges.

Mistake 3: Forgetting that the cross axis flips with flex-direction

In a row layout, the main axis is horizontal and the cross axis is vertical. In a column layout, the axes swap: the main axis is now vertical and the cross axis is horizontal. This means justify-content: center in a column layout centers items vertically (along the column), and align-items: center centers them horizontally (across the column).

Mistake 4: Using flexbox for grid-like layouts

If you find yourself fighting flexbox to get items to align in a strict grid — giving every item the same fixed width, preventing uneven last rows — you probably want CSS Grid. grid-template-columns: repeat(3, 1fr) enforces a strict three-column layout that flexbox cannot achieve without hacks.

The gap Property in Detail

The gap shorthand accepts one or two values: gap: 16px sets equal row and column spacing; gap: 8px 24px sets 8px between rows and 24px between columns. You can use any CSS length unit — px, rem, em, vw, or percentages. A value of 0 removes all spacing.

A subtle but important fact: gap only applies between items, never outside them. If you need spacing between the container edge and the first/last item, use padding on the container instead. Combining padding on the container with gap between items is the cleanest pattern for card grids and toolbars.

Controlling Individual Items: flex-grow, flex-shrink, and flex-basis

The generator handles container-level properties, but flex items have their own three properties that control how each item sizes itself relative to its siblings. All three are combined in the flex shorthand:

• flex-grow — a unitless number that determines how much of the free space a flex item claims. A value of 1 on every item splits free space equally; a value of 2 on one item gives it twice as much free space as siblings with 1. Default is 0 (items do not grow).
• flex-shrink — controls how much an item shrinks when the container is too small to hold all items at their ideal size. The default is 1, meaning all items shrink proportionally. Setting flex-shrink: 0 on an item prevents it from shrinking — useful for fixed-width sidebars or logos.
• flex-basis — sets the item's ideal size before flex-grow and flex-shrink are applied. It works like width in a row layout and height in a column layout. Use flex-basis: auto (the default) to size the item from its content, or a length like 200px or 50% for an explicit starting size.

The most commonly used shorthand values are: flex: 1 (equal share of all available space), flex: 0 0 auto (fixed size, no grow or shrink), and flex: 1 1 280px (start at 280px, grow and shrink freely — the responsive card pattern). The W3C recommends always using the shorthand flex instead of individual properties because the shorthand sets sensible defaults for the other two values automatically.

Browser Support

CSS Flexbox has been supported in all major browsers since 2015. The gap property for flexbox (distinct from the older Grid-only grid-gap) has been supported since Chrome 84, Firefox 63, Safari 14.1, and Edge 84 — safe to use without fallbacks in all modern environments. You only need to worry about flexbox fallbacks if you still need to support Internet Explorer 11, which has a partial and buggy implementation.