I managed to hide the background of the seperator between open windows by using:
hi VertSplit term=NONE cterm=NONE gui=NONE guifg=NONE guibg=NONE ctermfg=NONE ctermbg=NONE
fillchars still show up, and from my research it seems like its impossible to completely remove the
fillchars. I figured there must be a way to make it
fillchars invisible, but I cant seem to figure out how.