Remove padding from certain index pages

Site URL: https://parrotfish-cymbals-axkd.squarespace.com/

Hi there, 

I have a few Index pages (sub-pages?) where I want remove the padding so that the content is full screen. 

I'm currently using the id's of the Index Pages (like below), and it works temporarily, but the id's keep changing and then the code stops working. 
#yui_3_17_2_1_1580574561775_504.Index-page-content
{
  padding-top: 0;
}

I've tried replacing the ids and go the #page-title route, like below but that just isn't working at all. 
#Instagram .Index-page-content {
  padding-left: 0;
  padding-right: 0;
  padding-bottom:0;
  max-width: 100%;
}

I've also tried adding this code to the page header, and while it works if I place it on the Index page, it won't work if I place it on the sub-index page. 
<style>
  .Index-page-content {
    max-width: 100% !important;
    padding-left: 0;
    padding-right: 0;
}
</style>

What am I missing?!

Website url is 
https://parrotfish-cymbals-axkd.squarespace.com/

and password is localforeigner

<style>
.Index-page .Index-page-content {
    width: 100%;
    max-width: 100%;
    padding-left: 0;
    padding-right: 0;
}
</style>

Add to Page Header

Great, but is there anyway to make this work on a specific index subpage? Adding this to the header of one of index pages sub pages does not work?

13 hours ago, Bram said:

Great, but is there anyway to make this work on a specific index subpage? Adding this to the header of one of index pages sub pages does not work?

Can you share link to a subpage?