常见class关键词: 布局类:header, footer, container, main, content, aside, page, section 包裹类:wrap, inner 区块类:region, block, box 结构类:hd, bd, ft, top, bottom, left, right, middle, col, row, grid, span 列表类:list, item, field 主次类:primary, secondary, sub, minor 大小类: