11.2. Table Cell Borders

There are actually two quite distinct border models in CSS. The separated border model takes effect when cells are separated from each other in layout terms. The other option is the collapsed border model, in which there is no visual separation between cells, and cell borders merge, or collapse, with each other. The former is the default model, although in an earlier version of CSS the latter was the default.

An author can choose between the two models with the property border-collapse.