borderimagewidth

Borderimagewidth is a CSS property that specifies the width of the individual images used in creating a custom border for an element. When you use the `border-image-source` property to define a border made from an image, the `border-image-slice` property is used to divide that image into nine regions. The `border-image-width` property then controls the width of the four corner regions and the four edge regions of this sliced image, effectively determining how much of each image segment is used to form the border.

This property allows for precise control over the rendering of image-based borders. For instance, you could set a wider width for the side images compared to the corner images, or vice versa. The values for `border-image-width` can be specified using various CSS units, including pixels, percentages, or ems. It can also accept keywords like `auto`, which attempts to calculate the width based on the `border-width` property. If `auto` is used and the `border-width` is not set, then `border-image-width` defaults to the value of `border-width`. If `border-width` is also not set, it defaults to `1`.

The `border-image-width` property works in conjunction with `border-image-source`, `border-image-slice`, `border-image-repeat`, and `border-image-outset` to create complex and customizable borders that go beyond the capabilities of standard CSS borders. It is particularly useful for creating decorative borders for web page elements that require a unique visual style.