Adguard is free and supports custom elements. As a bonus, it’s open source. These are the rules I use:
www.reddit.com##.xpromopill
www.reddit.com##.active.xpromopopup
www.reddit.com##.amp.snackbar
www.reddit.com##.navframe > .xpromominimal.dualpartinterstitial
www.reddit.com##.xpromoadfeed