Translation:Ano, dobrý den.
Install a Czech keyboard layout or some other layout that contains this character. Every phone keyboard app is different.
Yes, I would agree with you. If it wasn't for the fact that you give Hello as a default translation for both in other sentences. That is Dobrý den and Dobrý večer. It's the inconsistency of it, that I don't like. And if you accept it in one direction, it should go both ways. Or, you should remove Hello as a translation for Dobrý den and dobrý večer.
Essentially, you need to memorize/absorb declension tables, which indicate how the form of a word differs based on its use. In the case of adjectives, their form differs based on the gender, number, and case of the nouns that they modify. The chart at the link that follows will give you an idea of how dobrý changes, and you can look up pretty much any word there as well: https://en.wiktionary.org/wiki/dobr%C3%BD. It can be confusing at first, but repeated practice of the lessons here will definitely help.
Dobry is masculine, dobre is neuter, changes according to the noun it's in front of. Dobra is feminine. Not sure if that last one (dobrou) is a form or not, I'm not that far yet XD
If someone else could answer though that would help both of us :) I looked it up on google translate and it said "good night" for some reason