How to Round Corners in CSS

Set equal width and height, then apply border-radius: 50%. For example: width: 100px; height: 100px; border-radius: 50%;

50% creates an ellipse based on the element's dimensions (circle if equal). 9999px is a large fixed value that creates a pill shape regardless of dimensions - useful for buttons with varying widths.

Use the shorthand with 4 values (top-left, top-right, bottom-right, bottom-left): border-radius: 10px 10px 0 0; or individual properties like border-top-left-radius: 10px;