Given the size and overall appearance Galerina is a plausible suggestion for this sighting, though there are several other genera of small, brown mushrooms. Thank you for the view of the underside, which shows that each gill has a white, fringed edge. In this genus, there are elongated, colourless cells along the gill edge and, though you’ll only see those cells under a microscope, in mass they give the gill edge that whitish, uneven, fringed look. Galerina is not the only genus to have such cells, so by itself a fringed gill edge is not conclusive evidence, but it is very useful additional evidence in favour of Galerina.