CSSonly

CSSonly refers to techniques that create interactive user interface behavior using only CSS, without writing JavaScript. In CSSonly approaches, styling rules, selectors, and CSS variables render dynamic states such as opened panels, navigation menus, or image carousels, using mechanisms like the :target pseudo-class, the :checked state of input elements, and sibling selectors. Common tools include the checkbox or radio button hacks, label associations to toggle state, and focus-related selectors like :focus-within to reveal content when a control or container receives keyboard focus. Advanced patterns may also employ CSS animations and transitions to enhance perceived interactivity.

Typical applications include accordions, tabs, modal-like panels, dropdown menus, and simple content sliders. The :target trick enables in-page navigation by changing the URL fragment to reveal a section, while the :checked approach uses a hidden checkbox to control visibility of adjacent content. CSS variables allow theming and state-based styling across components, enabling cohesive CSSonly UI without script.

CSSonly techniques offer benefits such as reduced JavaScript dependency, potentially faster rendering for simple interactions, and a straightforward progressive enhancement path. However they come with notable limitations: there is no true data processing, no server interaction, and complex behaviors or dynamic content generally cannot be implemented. Accessibility considerations are essential, as screen readers and assistive technologies may not expose CSS-only state changes reliably, and keyboard navigation must be carefully designed to be intuitive.

In practice, CSSonly is best used for simple, self-contained UI states or as an enhancement layer, with JavaScript available to handle richer interactions, data-driven behavior, or accessibility-critical features.