CSS corner-bottom-shape Property

The corner-bottom-shape property provides a declarative way to control the exact geometry of an element’s lower corners without rewriting the whole outline. Instead of a single uniform radius or a generic clip, it lets a designer define distinct shapes for the bottom-left and bottom-right corners - from soft rounded contours to sharp bevels, notches, chevrons or concave arcs - and have those shapes applied to the element’s painting and hit-testing boundaries. Because it targets only the lower corners, it is ideal for visual patterns where the top of a box remains regular while the bottom needs custom treatment (for example conversational bubbles, cards with notched footers, or decorative callouts).

When used in combination with other box-related rules it composes predictably: the shapes defined by corner-bottom-shape influence how the element’s background and border are painted and how overflow is clipped, much like how background-clip and border-radius affect painting. If you need more complex silhouettes or non-rectangular text flow, it can be used together with clip-path or mask-image - use corner-bottom-shape when you want a concise semantic way to target only the bottom corners and maintain simpler layout boxes, and prefer the other tools for full arbitrary masking or complex polygon clipping.

The property is intended to animate smoothly so it works well in transitions and micro-interactions; pairing changes to corner-bottom-shape with transforms produces polished effects where a card or panel morphs its lower corners while scaling or moving. For such animated uses, you should be mindful of repaints and compositing costs: complex corner geometry may force the browser to re-rasterize the element, so combine with layout-friendly techniques like transform for motion and limit frequent heavy updates.

For robustness and accessibility, treat corner shaping as a decorative enhancement rather than a replacement for semantic cues. Provide sufficient contrast and spacing so interactive targets remain large enough despite visual clipping, and offer fallbacks (for example a plain rectangular presentation) in contexts where the decorative corners might interfere with content legibility or printing. When designing, prefer subtle shapes for dense interfaces and reserve dramatic bottom corner treatments for cases where the shape supports the content’s meaning or visual hierarchy.