GRASS-files are used in the Neo4j Browser to style nodes and relationships of a Neo4j graph.
GRASS stands for Graph-Stylesheet and lets one define a visual style for both nodes and relationships to be used within the Neo4j Browser to customize the visual appearance of a graph.
Each node- and relationship label can have it own visual style assigned to wheres inheritance is also supported. A GRASS-file contains general super-style named "node" and "relationship" which are used to inhere properties to sub-nodes and sub-relationships.