'System' theme - gone in latest update?

I have just updated to the lastest version of emClient on my laptop and haven’t yet done so on my main desktop work computer. I used to use the appearance theme called “system” and still do on my desktop, but, alas, I see it isn’t an option on the updated laptop and I’ve been automatically moved to another one. Where has ‘system,’ theme gone? Is there a way I can save the theme I’m currently using on my desktop and re-install it on my laptop (and on my desktop after updating emClient)?