[Reg 5.12->5.13] Offline documentation misses separators for sections & method descriptions

The online documentation separates methods by a horizontal line and the overview sections are well recognized because of the tables. These are completely gone in the offline documentation for Qt 5.13, which makes it pretty hard to browse for e.g. some specific method, or for the "detailed description".
The offline documentation of earlier Qt versions had a gray background for the headings & methods, which arguably did not look very beautiful, but performed its job.