订阅以下载
flat world with changeable floor material and full CSM support

(I didn't know gm_black_v3_colourable existed)

in-game name is gm_flatanything

experimental map which was made in a couple of hours, i can make variations such as night version if anybody wants it

ground is func_brush which can be edited in various ways. you can apply any available material to it, change colors or even remove it if you like
skybox ground has to be edited separately, it's best to remove it when using map with CSM since it's completely unlit

stuff you might want to use with this:

Real CSM - Modern Lighting & Shadows https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=2817072898

Material URL tool https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=2559426779

Converted HL2 map materials https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=2810344748