Question: Due to impermanance of everything, Are there anything to be happy or sad about ? Even about **dhamma** ?

If something seems like to be happy, there are some reasons to not to be happy.

1. It is impermanant for sure. but also,
2. That **happiness make sadness in the future (future includes next lives)** (I need to be sure about this sententce, please mention about this in your answer)

Are enlightened people happy ? Or neither happy nor sad ?

Answer: 
I think Buddhism recommends you focus on what's virtuous and moral instead of on what's feels pleasurable.

For example, lying, killing, stealing -- are all to be avoided -- and that's important.

Conversely, generosity, kindness, keeping your promises -- that's important too.

There is a word -- [sukha](https://en.wikipedia.org/wiki/Sukha) -- which might be translated "happiness". It's used in contexts like the [Sukhavagga](https://www.accesstoinsight.org/tipitaka/kn/dhp/dhp.15.budd.html).

I suspect it's a happiness conditioned or caused by an absence not by a presence -- for example not happiness because you have something ("a chocolate bar") but happiness because of not having something ("anger", "greed", "remorse").
yes you can care about 4 ''karmas'', with the last one being the intention to get enlightened, ie not getting any birth

> 
> And of what sort, brahmin is the deed that is neither dark nor bright,
>  with a result that is neither dark nor bright, which, itself a deed,
>  conduces to the waning of deeds?
> 
> 
> In this case, brahmin the intention to abandon this dark deed with its
>  dark result, the intention to abandon this bright deed with its bright
>  result, the intention to abandon this deed both dark and bright with a
>  its result both dark and bright, - this intention is called "the deed
>  that is neither dark nor bright, with a result that is neither dark
>  nor bright, which, itself a deed, conduces to the waning of deeds."
> 
> 
> These four deeds I have myself comprehended, realized and made known."
> 
> 
> 

<https://obo.genaud.net/dhamma-vinaya/pts/an/04_fours/an04.232.wood.pts.htm#p1>