width100

Width100 is a term used in web design and software development to denote an element that spans the full width of its containing block. It is not a formal standard, but a descriptive label applied in documentation, design systems, and codebases.

In CSS, a typical implementation is width: 100%;, often paired with display: block (or inline-block for some element types) and box-sizing: border-box to ensure padding and borders are included within the width calculation. The effect is an element that stretches to the container’s width.

In many CSS frameworks and UI libraries, width100 (or an equivalent utility such as w-full) provides a shorthand way to set an element’s width to its container. The exact class name and behavior vary between frameworks and projects.

Practical considerations include how the width interacts with padding, borders, and margins, as well as responsive behavior within fluid layouts. When the parent container resizes, elements using width: 100% typically adjust accordingly, provided no conflicting constraints are present. Images and videos often use width: 100% with height: auto to maintain aspect ratios.

See also full width, max-width, container, and responsive design utilities.