.container {
background-image: url("img/rose.jpg");
height: 800px;
}
/* Check Path to image, in this case, its in a folder called img */
/* Check if you Linked your css File on your header, you Link it in the
Header like this <link rel="stylesheet" href="main.css"> */
/* Check if the Name of your Image is the same like how you saved it */
background-image: url(nickcage.jpg); // first problem may be missing quotation mark
// Second may be wrong path
// check the name of the file if there is any error
// check whether you are using proper extension of the file background-image: url(nickcage.jpg); // No quotes around the file name so just write it down without "nickcage".jpg