pasted Block ID= syntax error

I downloaded the Chrome extentions, restared Chrome, clicked the "B" button, copied the code for the block of text that I want to give a colored background, went to Design, CSS and pasted the code:

#block-yui_3_17_2_1_1585239523934_56605

then it says syntax error on line 1 and nothing happens
 

This is for a blog post on my site. 

Your code should be

#block-yui_3_17_2_1_1585239523934_56605 {
	background: green;
}

thank you, the rando stuff I found online didn't show the code