html5 – Change the CSS of a file uploaded from a website

Hello hello, I'm trying to change the background image, but I'm taking this from a URL that can't be changed. Is there any other way to do this from the same file i run it in?

    .treeTable tr.collapsed.selected td a.expander, .treeTable tr.collapsed.accept td a.expander {
  background-image: url (../ images / toggle-expand-light.png);
}

.treeTable tr.expanded.selected td a.expander, .treeTable tr.expanded.accept td a.expander {
  background-image: url (../ images / toggle-collapse-light.png);
}