A block is a thing. A groove is a relationship. Once those two are fixed, most technical diagrams are a matter of arranging them — and the reader never needs a legend.凸块是一个东西，凹槽是一种关系。这两样定下来之后，多数技术框图就只是怎么摆的问题 —— 而且读者永远不需要图例。
Drawing diagrams in this style needs two things the control kit does not give you. Connectors are grooves — inset, so the line reads as cut into the surface rather than laid on top. And arrowheads and stroke ends are raised with a paired filter: drop-shadow(), because an SVG stroke does not take box-shadow at all — the recipe that lifts every HTML block has no effect on the element a diagram is mostly made of.用这个风格画框图，要多两件控件集里没有的东西。连线是凹槽 —— 加 inset，线就读作刻进面料，而不是搭在上面。箭头和线端靠成对的 filter: drop-shadow() 浮起，因为 SVG 描边根本吃不到 box-shadow —— 那个把每个 HTML 方块顶起来的配方，对框图里占比最大的元素完全没作用。