Add shadow styles for Safari

[gissoo]

Rebecca's notes on shadow styles supported by Safari:

docs: https://developer.mozilla.org/en-US/docs/Web/SVG/Element/feDropShadow), and in a quick test and i found that Safari does render this.

Gissoo to create an SVG export from Figma that has all the drop shadow filter definitions needed (one for each leaf color, one for plaque hover, one for plaque selected).

[rlskoeser]

Note that it should be feasible to apply svg filters using css. See https://www.stefanjudis.com/today-i-learned/svgs-filters-can-be-inlined-in-css/

So if we can create the filters we want, it should not be too much additional work to adjust the CSS to use svg filters. We'll have to test on the various browsers to make sure this change doesn't introduce new problems, though.