Trouble customizing style via css

Really interested in this plugin but I can’t seem to customize certain things I thought should be basic.

For example I’m noticing for the login form, all the title text (username, firstname…etc) AND input fields are all grouped into one big row and one column. As a result I can’t seem to nudge the title texts a few pixels down to align better with the input fields next to their right. When I try it breaks the layout. I’m having other similar issues like this where I cannot make simple nudges without breaking everything.

To make matters worse, it seems as though I can’t even target individual elements like just the Username field or just the Lastname field…etc. If I could do that maybe I can move things around that way.

I wish at the very least the HTML was organized and subdivided within more rows & columns kinda of like Bootstrap so that I can at least move “groups” around like all the text titles or all the input fields…etc.

I”m not the best html/css guy so I could be totally missing something here. Would love to hear what your comments are on this. I need some serious help. If I can get wp-members plugin or any plugins for that matter to be POSITIONED the way I need them to look so it’s in harmony with my site, then this whole WordPress thing is not gonna work for me.

Any help would be appreciated.

http://wordpress.org/plugins/wp-members/