What Is CSS Border Radius?
The CSS `border-radius` property rounds the corners of an element's outer border edge. It can be set uniformly for all four corners, or individually for each corner. The advanced shorthand allows you to even set different horizontal and vertical radii for each corner, creating elliptical corner shapes for organic, blob-like designs.
```
`/* All corners equal */
border-radius: 8px;
/* Individual corners (top-left, top-right, bottom-right, bottom-left) */
border-radius: 8px 4px 8px 4px;
/* Elliptical corners (horizontal / vertical radii) */
border-radius: 40% 60% 70% 30% / 40% 50% 60% 50%;
/* Perfect circle */
border-radius: 50%;`
## How to Use the Border Radius Generator Online
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## Key Features
- **Visual handle-based editing**: drag corners directly on the preview.
- **Individual corner control**: set each of the four corners independently.
- **Elliptical radius support**: X and Y radius values for each corner.
- **Unit selection**: pixels, percentages, em, rem.
- **Presets**: common values like "card", "button", "pill", "circle".
- **Background and border color preview**: see the element as it would appear in your UI.
## Use Cases
### UI Components
Different UI components have different conventional corner radii: cards use 8–16px, small buttons 4–8px, large pill buttons use 999px or 50%, avatars use 50% for circles. The generator lets you quickly experiment and find the right value for each component.
### Blob and Organic Shapes
The advanced elliptical radius syntax (`border-radius: 40% 60% 70% 30% / 40% 50% 60% 50%`) creates irregular, organic blob shapes used in modern web design for decorative elements, background shapes, and image frames. The visual generator makes these complex values approachable.
### Creating Consistent Design Systems
Design systems define a limited set of border-radius values (e.g., sm=4px, md=8px, lg=16px, full=9999px). The generator helps establish these values visually before encoding them as CSS variables or Tailwind config values.
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## Frequently Asked Questions
### What's the difference between border-radius: 50% and border-radius: 9999px?
50% makes the element a perfect circle if it's square, or an ellipse if rectangular. 9999px (or any very large value) creates fully rounded short ends while leaving long sides straight — the "pill" shape. Use 50% for avatars, 9999px/999px for pill buttons.
### Can border-radius create a triangle or other polygons?
Not directly — border-radius only creates rounded corners. CSS triangles are created using the border trick (a zero-width/height element with borders on specific sides). For complex polygons, use `clip-path` instead.
### Does border-radius affect the border's appearance?
Yes. `border-radius` rounds the border along with the background and content area. The border follows the rounded corner exactly.
### Can I animate border-radius?
Yes. CSS transitions and animations on border-radius are GPU-accelerated in modern browsers, enabling smooth morph animations between shapes. Keep transitions short (200–400ms) for best performance.
### Is the tool free?
Yes, completely free with no signup required.
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*Originally published at [aiforeverthing.com](https://aiforeverthing.com/blog/css-border-radius-guide)*
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