I am looking for a LMS with the possibility to customize it very easily

There are a few LMS on themeforest with a lot of features. However the design is always not what I am looking for. I am searching a LMS with the possibility displaying onsite/offline courses and buddypress features.
What I can’t test is the possibility of changing the design (for e. g. buttons, colors, spacing, etc) of the theme without much coding adventures. I am familiar with CSS but I won’t spend a lot of time with coding.

Is there a LMS theme out there with some back end functionalities which allows customizing the theme very easily?

It all depends what is for you easily? The best is to contact template developers. They will tell you from first hand.