Adjust popup size

good afternoon to know if there is any way to adjust the size of the pop-ups and I would like to adjust so that all four are seen as if it were a menu of four boxes and not down as in list

this is the code he used

Actividad 1
{iframe src=“”}

Actividad 2
{iframe src=“”}
but when I select another marker when I go back to the bookmark, only one image or video appears

this is the map that I am working