Analyse the given text to identify the key theme.
The moonlit night was serene and peaceful.
The key theme of the given text is tranquillity.
Complete the following task based on the instruction and optional input provided.### Instruction:
Analyse the given text to identify the key theme.

### Input:
The moonlit night was serene and peaceful.

### Output:
The key theme of the given text is tranquillity.