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=“https://www.youtube.com/embed/z7VYVjR_nwE”}

Actividad 2
{iframe src=“https://www.youtube.com/embed/z7VYVjR_nwE”}
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