There is a reason why to use alias token for surface (backgrounds). If you just use neutral-100, neutral-200... for background it would be OK just for light mode. But on dark mode you have to care about elevation. For ex. On light mode UI, popover or dropdowns have pure white (neutral-0), But on dark mode you can't make it pure black. it should be neutral-200 (a bit gray) makes look elevated. Another example: On light mode, if you use gray background (neutral-200) and cards with white bg (neutral-0), that will look like cards are closer to you. But on dark mode, if you flip colors, it will be unrealistic. Check my design system finalui.com for better understanding