Breakdown of Das ist sehr lieb von dir.
sein
to be
sehr
very
dir
you / to you [informal singular, dative]
von
from, of / by (agent in passive clauses)
Questions & Answers about Das ist sehr lieb von dir.
Why is dir used here instead of dich or du?
The preposition von always requires the dative case. Because of this, you must use dir, which is the dative form of du.
I usually see lieb used to mean "dear" or "sweet". Does it just mean "kind" here?
Exactly. While lieb is often used as "dear" in a letter or to describe someone as "sweet", in this specific phrase it translates to "kind" or "nice". You could also say Das ist sehr nett von dir to mean the exact same thing.
Could I use Es instead of Das at the beginning of the sentence?
Yes, you could say Es ist sehr lieb von dir (It is very kind of you). However, using Das (That) is extremely common in spoken German because it strongly points to the specific nice thing the person just did.
How would I change this to say "That is very kind of him"?
You just need to change the pronoun after von to the dative form of "he", which is ihm. The sentence becomes Das ist sehr lieb von ihm.