You just need to brush up on addressing URL
./ means look in the current directory.
.. / means to rise to a higher level and to look there.
Let's assume this structure (you its not shown, you have to wonder):
then you should write in index.html the address of the image:
and in styles.css:
Well, or if you know all this, it is possible to start the server not from the root folder of the project, and set up some internal.