This is the 17479th most frequent Russian word.
тонких
"Тонких" means "thin" or "subtle" in English, depending on context.
Here, "тонких" describes the quality of the fabrics being thin, attributing a characteristic to the noun "тканей" (fabrics).
Она носит платье из тонких тканей.
She wears a dress made of thin fabrics.
In this sentence, "тонких" qualifies "линий" (lines), referring to their slim or fine nature in a descriptive manner.
На картине можно увидеть детали тонких линий.
In the painting, details of thin lines can be seen.
Here, "тонких" is used metaphorically to describe the slight or subtle differences, applied to "различий" (differences) indicating their minimal or nuanced nature.