It's because any list item in the #main_content div should 0.833 times the size of its parent. To prevent this inherited shrinkage, use this selectorset
这是因为 #main_content div 中的列表项应当是其父字体大小的 0.833 倍。
2
File set: the UMF files that comprise a specific load, those files meet the criteria set by the Selector (e.g. file name, date, data source, etc.).
文件集：包含特定加载的UMF文件，这些文件满足选择器的标准集(即文件名、日期、数据源等)。
3
So the return value (sort of a misnomer, but still a useful way to think about things) for an attribute selector is a value; for an element, it's a node set (containing a single node).