Hi,
The X icon is not visible, because it’s color is set to green, and the search width is hovering over it. I suggest changing the search bar width on mobile devices to a smaller one, like 80% or so, and also changing X icon color to the default white – that should be somewhere in the theme settings.
That URL seems to be correct now, it contains the search override parameters. If it still does not override the results, then the theme might not support that, although it is very hard to tell. If you have any other search plugins active, such as Relevanssi, SearchWP or anything, that could also override the results.