Free online developer tools
Free online CSS generators that run in your browser. Build gradients, box shadows, rounded corners, flexbox and grid layouts, pick colors, and beautify or minify code. Live preview and copy-paste CSS, no sign-up.
Create CSS gradients.
Create CSS shadows.
Generate border radius CSS.
Create flexbox layouts.
Generate CSS grid layouts.
Pick and convert HEX, RGB, and HSL colors.
Format or minify CSS code.
Compress HTML to reduce file size.
The choice is not about preference — the two tools solve different shapes of problem, and the fastest way to pick is to ask whether you are laying out along one axis or two.
Flexbox is one-dimensional. It arranges items along a single axis — a row or a column — and is content-driven: items size themselves from their content while you distribute the leftover space. Reach for it for a nav bar, a toolbar, a row of buttons, or centering one thing inside another.
Grid is two-dimensional. It controls rows and columns at the same time and is container-driven: you define the tracks and place items into them, so things line up across both axes. Reach for it for page and section layouts, card galleries, or any design where alignment has to hold vertically and horizontally at once.
They are not rivals — they compose. A grid item can be a flex container, and a flex item can be a grid. A practical rule: use Grid to define the overall structure, and Flexbox to arrange the items sitting inside one cell or one row of it.
box-shadow is expensive to paint, and animating it forces the browser to repaint
every frame, which drops frames on lower-end devices. The fix is to animate compositor-only
properties instead — transform and opacity run on the GPU without
triggering a repaint. A common pattern is to render the larger shadow on a pseudo-element and
animate its opacity from 0 to 1, so the shadow appears to grow on hover without any
per-frame repainting.
border-radius accepts an optional / that separates horizontal from
vertical radii. border-radius: 50px / 20px gives every corner a 50px horizontal
radius and a 20px vertical radius — an ellipse, not a circle. The full eight-value form,
border-radius: a b c d / e f g h, sets all four horizontal radii before the slash
and all four vertical radii after it, which is how the organic "blob" and squircle shapes are
built.
A gradient interpolates between its colors through a color space, and the default
sRGB interpolation passes through a desaturated, muddy grey when the two endpoints
sit far apart on the color wheel — blue to yellow being the classic case. That washed-out
midpoint is the "grey dead-zone." CSS Color 4 lets you choose the interpolation space to avoid
it: linear-gradient(in oklch, blue, yellow) interpolates through a perceptual space
and keeps the mix vivid, and in hsl travels around the hue wheel instead of cutting
through grey.
Use Flexbox for one-dimensional layouts — a single row or column such as a nav bar or a group of buttons — where items size from their content. Use Grid when you need to control rows and columns together, like a page layout or a card gallery that must align on both axes.
Yes. They nest and compose freely: a Grid item can be a flex container and a flex item can be a grid. A common approach is Grid for the overall page structure and Flexbox for arranging the contents of individual cells.
Animating box-shadow forces a repaint on every frame, which is costly. Animate transform and opacity instead — they are handled by the compositor on the GPU. A common trick is to put the shadow on a pseudo-element and fade its opacity.
It separates horizontal and vertical radii to create elliptical corners. border-radius: 50px / 20px makes each corner 50px wide and 20px tall rather than a quarter-circle. The eight-value form lists all horizontal radii before the slash and all vertical radii after it.
By default a gradient interpolates in the sRGB color space, which passes through a desaturated grey when the two colors are far apart on the color wheel. Interpolate in a perceptual or hue-based space instead, for example linear-gradient(in oklch, blue, yellow), to keep the transition vivid.