For one input field on a form, there are around 6 to 12 different CSS files supplying rules including inline styles. The sane answer is to convince the client to migrate to another solution or recreate, but assuming this is like your spouse's beloved pet that you MUST operate on or else it will die, how do you begin to make sense of it all?
His solution was
- to replicate the whole layout of existing theme from scratch
- produce the exact functional behavior of previous theme
- on finish, he will simply going to get rid of the unnecessary plugins
It can be a bit intimidating, but if you know what you are doing, it will be worth the effort.