Workaround selected item icon not shown in IE11

[web-padawan]

Fixes #38

Depends on vaadin/vaadin-list-mixin#42

For some reason, in IE11 items do not pick up the CSS custom property defined on the list-box element. This change workarounds that, without it ::before pseudo elements never appear.

Note that this also needs calling updateStyles(): without that, the original issue on the GIF happens IE11 (::before pseudo elements only appear on hover).

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This change is 

[yuriy-fix]

Reviewed 1 of 1 files at r1.
Reviewable status: complete! all files reviewed, all discussions resolved

[manolo]

Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @web-padawan)

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theme/lumo/vaadin-list-box-styles.html, line 37 at r1 (raw file):

      }

      /* TODO(web-padawan): a workaround to display checkmark in IE11 when not used in dropdown-menu */

What means this TODO? This sentence is not clear to me if you need to figure-out a workaround or you need to remove this workaround

[web-padawan]

Reviewed 1 of 1 files at r2.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @web-padawan)

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theme/lumo/vaadin-list-box-styles.html, line 37 at r1 (raw file):

Previously, manolo (Manuel Carrasco Moñino) wrote…

What means this TODO? This sentence is not clear to me if you need to figure-out a workaround or you need to remove this workaround

Updated the comment to remove TODO, as this is something we only can replace later once we refactor and introduce "unselectable" list-box, which is not planned at this point

[sohrabtaee]

There's a still a problem in IE11, before hovering on the items, the padding is not there.

[sohrabtaee]

[manolo]

Reviewable status: complete! all files reviewed, all discussions resolved