VIM E518: Unknown option: dark -

i configuring vim colorscheme these in .vimrc.

 "color scheme    syntax enable    set background = dark    colorscheme solarized 

when open file vim, reports:

error detected while processing /home/user/.vimrc:   line    3:   e518: unknown option: dark   press enter or type command continue   

but works picture: dark background

beacuse when comment in .vimrc:

 "set background = dark   

the monitor this:commented dark background.
want know why happen , how fix it.

valid syntax :set:

set option=value set option= value 

valid syntax :let:

let variable=value let variable= value let variable =value let variable = value 

it recommended use same syntax consistency. use:

set option=value let variable = value