In this particular template the designers have elected to space all content out more. You can negate that with this...
.platform-content {
margin: 0;
padding: 1rem;
}
But that will effect all viewport sizes. You could even set padding to zero but you may then find that some elements overlap as other aspects of the design of this template use negative margins for other content.
You cannot change this specifically on the "hidden" content because the container is the parent of the "hidden" content and the padding is on the parent - there is no CSS command that will zeroise padding/margins on a prent container dependent upon the child content.
Regards, Mark.