This appears to be a springtail (Collembola). I'm not familiar with Sri Lankan fauna, but the overall body plan (kind of oval, pudgy, short-legged) reminds me of a subgroup of springtails, the Poduromorpha.
You can see similar-looking species in the Superfamily Neanuroidea, which are an example group in the Poduromorpha order:
Brachystomella parvula from UK; Credit: Andy Murray (2012); Source: Wikimedia
Red Poduromorph Springtails (family Neanuridae) ; Credit: Elahi Rayan (2018); Source: Wikimedia