Tomato seedling disease

Good afternoon
This year, when growing tomato seedlings, the following infection was noticed on the leaves (see photo).
It appeared almost instantly (it wasn’t there yesterday afternoon, but today it was in all its glory and in large quantities).
Now there are about 100 seedlings on the windowsills, of which 25 are infected, not nearby, but in different parts of the window sills (although this may be due to the fact that I rearrange them closer/farther from the light for uniform growth).
Tell me, what kind of attack is this and how can I fight it? I tried to search using pictures in search engines - it didn’t bring much results, everything seems different. I really feel sorry for the harvest