I can't remember what the default is but a custom theme is when a subreddit uses CSS code to alter what their sub looks like. As an example, this is what /r/abroadinjapan looks like with a basic theme: https://gyazo.com/8beecfaa99dabd45ee963fc644c60577 and with no theme: https://gyazo.com/31f7bba0ff6bc0cf06fd1413d48f0c04 I plan on making a custom theme so that /r/abroadinjapan looks better than it currently does but I wanted to see how much of an impact it would have. A lot of big subreddits use them but some don't, some even use CSS code to stop you downvoting which I dislike and won't be doing. So, how much effort should I put into the theme? Do have themes turned on or off? Do you even care?