userstyle

Userstyle is a user-authored stylesheet, usually written in CSS, that changes the appearance of websites or applications without altering their core functionality. Userstyles are applied through browser extensions or built-in user style systems and can adjust colors, typography, spacing, layout, and element visibility. They are commonly used to apply themes, improve readability, or tailor a site to individual preferences or accessibility needs.

Creation and application: A userstyle targets specific URLs or domains using CSS selectors and rules. It may include metadata such as a name, author, and description. Styles are loaded by extensions such as Stylish, Stylus, or by browser features that support user styles. Public collections exist on community sites, and users can also write and host their own styles. Styles are typically scoped to particular sites but can be global.

History and ecosystem: The concept emerged with early browser customization and gained prominence with extensions that manage user styles. Notable tools include Stylish and Stylus, with community repos hosting thousands of styles. Some platforms have changed policies or deprecated features due to privacy concerns, leading to forks and alternative managers. Styles are usually shared under permissive licenses, but terms vary by repository.

Limitations and considerations: Userstyles depend on the structure of the target site and may break when sites change their markup. Applying styles can affect accessibility or functionality if not carefully designed. Extensions with broad page access raise privacy considerations, and users should obtain styles from trusted sources and review permissions.