[bug] Fix for addon-cssresources till scrollbars are properly addressed

[pgoforth]

The absolute positioning caused by 79d2cd1#diff-77ef954da6ec85c57634e9e3c9cc9750 made the css resources tab contain overlapping source files:

The solution was to render them into a container instead of a <Fragment>

[ndelangen]

A test needs to be updated:

 FAIL  addons/cssresources/src/css-resource-panel.test.js
  ● CSSResourcePanel › constructor › should not render anything

    Expected <CssResourcePanel> to be empty render (false or null), but it was not
    Found Nodes HTML output: <div></div>

      57 | 
      58 |     it('should not render anything', () => {
    > 59 |       expect(node).toBeEmptyRender();
         |                    ^
      60 |     });
      61 |   });
      62 | 

      at Object.toBeEmptyRender (addons/cssresources/src/css-resource-panel.test.js:59:20)

@pgoforth Are you able to do this?

[pgoforth]

I can do that @ndelangen

Edit: All done @ndelangen

[shilman]

@pgoforth Still getting an error in CI:

 FAIL  addons/cssresources/src/css-resource-panel.test.js
  ● CSSResourcePanel › constructor › should render an empty div

    expect(received).toEqual(expected)

    Expected value to equal:
      true
    Received:
      false

      57 | 
      58 |     it('should render an empty div', () => {
    > 59 |       expect(node.matchesElement('<div></div>')).toEqual(true);
         |                                                  ^
      60 |     });
      61 |   });
      62 | 

      at Object.toEqual (addons/cssresources/src/css-resource-panel.test.js:59:50)

[pgoforth]

@shilman @ndelangen
Should be passing now