Change The Window Separator Border Color In Neovim

I use nvim-tree to show a directory tree in Neovim. A few of the colorschemes I use don't set the highlight color that makes the border between it and the main window show up. I make it visible by setting this in my init.lua file:

vim.cmd.highlight({ 
  "WinSeparator", 
  "guifg=#54546d guibg=#16161d" 
})

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