Since you need a list of all images and css files, ideally, you should pipe your output to something like:
Of course you could add more relevant extensions your project might contain, such as .bmp, for instance.
If I try
ls |grep -i '.gif$\|.jpg$\|.png$\|.css$' I get a list of all files in current folder with given extensions.
Let's take a closer look at this command:
$ ensures you won't match any undesired file, such as .css.bak.
$ matches end of line.
\| allows you to specify multiple patterns, so you don't need to invoke multiple
git ls-tree to get the whole list.
Should your repo contain any files with uppercase extensions you might want to add
-i in order to run grep case insensitively.
Patterns between single
' ensures dots are interpreted as dots, and not as "any character" as meant in regexes.