How do the descriptive details and sensory language like the dazzling emeralds and happy and prosperous people contribute to the mood of the story

By giving the reader a wider and broader sense of recognition of such object, person, emotion, you name it.

for example: the dog walked past me towards its owner. 
or
The beautiful brown labrador flounced past me towards its loving owner. 

It gives you more detailed information making the reading material more interesting, keeping the reader's attention. 
It contributes to the mood depending on what you say and how you say it.

for example: The solemn gray skies.
The gorgeous sparkling lights.