css background-image for main content area in WordPress

I have been trying to get a background-image to show in the main content area of a WordPress webpage. Inside the text portion of the WordPress editor, I’ve written a div tag with an id of “tour-icon”. Then inside the File Manager within cPanel, I have written a style.css file that has written code to show the background-image with a certain width but nothing happens except a change within the width of the main content area. I was able to do this before on another project but I don’t understand why it’s not working now. The code is the same as before. Does anyone know what I’m doing wrong?