Developer dashboard — Terminal glow

After importing the board, open it, then Settings → Design → Background → Custom CSS.
Paste this background value and click Apply:

radial-gradient(ellipse at 0% 0%, #243b59 0%, transparent 58%), radial-gradient(ellipse at 100% 100%, #163e3c 0%, transparent 55%), linear-gradient(145deg, #111c30 0%, #0b1423 58%, #101f2a 100%)

This is the built-in background setting, not theme/component CSS.
Backgrounds are stored separately and are not included in the current board JSON import/export.