Hi, so I am trying to change style of the first post in a new discussion with:
#content > div > div > div > div > div > div.PostStream-item:nth-child(1) {
backdrop-filter: contrast(0.9);
padding: 15px;
border-radius: 20px;
}

The issue that I am having with this is that when I resize the window of the page I get doubled scroll bar on the side like this:
this

Any ideas why this is happening and how I could fix this? Thanks

    f0rtem what browser and screen resolution does that happen on? I don't notice anything when I paste your code on a non-customized Flarum install. The placement of the scrollbars is between the stream and scrubber, or did you hide the scrubber? (the right panel with "x of x post")

    Firefox complains backdrop-filter isn't a valid property so I guess it's a different browser.

    P.S.1: #content > div > div > div > div > div > div.PostStream-item:nth-child(1) is functionally equivalent to .PostStream-item:nth-child(1) because the .PostStream-item class isn't used anywhere else in Flarum.

    P.S.2: .PostStream-item:nth-child(1) will target the first post in the stream, but that won't necessarily be the post number one if you start scrolling down and posts get unloaded. You can use .PostStream-item[data-number="1"] to target post number 1.