column-rule-width：<length> | thin | medium | thick
计算值：绝对长度值或者0（如果 <' column-rule-style '> 为 none 或者 hidden）
This module describes multi-column layout in CSS. By using functionality described in this document, style sheets can declare that the content of an element is to be laid out in multiple columns.
On the Web, tables have also been used to describe multi-column layouts. The main benefit of using CSS-based columns is flexibility; content can flow from one column to another, and the number of columns can vary depending on the size of the viewport. Removing presentation table markup from documents allows them to more easily be presented on various output devices including speech synthesizers and small mobile devices.