This is a defined behavior of border-collapse . Page 357 of the O'Reilly CSS Definitive Guide 3rd Edition says: if collapsing borders have ... ... <看更多>

border -collapse. Summary. Border-collapse can be used for collapsing the borders between table cells. Overview table. Initial value ... ... <看更多>

tables are generally prettier; you have 1px borders between cells; to style visually borders on the cell you have to style border-bottom of a ... ... <看更多>