Please post your queries with some details .
Please let me know the process To add New fields Values under Approval History Tab in SRM Request Details Form.--> Open Developer Studio and do the needful.
Under AR+System+Resource+Definitions we can see the Template SRS_ApprovalHistoryEntryTemplate.html which needs to be be updated as this hrml is used under Workflow.
You do not need to modify css or anything else.
This html file is called by active link (most of the time on hover event) using TEMPLATE or message tooltip action.
You just need to update this active link with the additional fields.
So capture the active link log and find out which active link is calling this html.
Please check below active link : SRS:RQD:Approval_Display (you will get some idea on how it works).