Material Design Polymer 2.0 Dropdown Menu (with multi-select).
Simple dropdown menu like paper-dropdown-menu, but drops "any kind of content" support in favour of multi-select.
Implemented as an simple combination of paper-input, paper-listbox and iron-dropdown.
Demo Link: https://www.webcomponents.org/element/IswPolymerElements/isw-dropdown-menu/demo/demo/index.html
<isw-dropdown-menu multi label="Dinosaurs">
<paper-item>Allosaurus</paper-item>
<paper-item>Brontosaurus</paper-item>
<paper-item>Carcharodontosaurus</paper-item>
<paper-item>Diplodocus</paper-item>
</isw-dropdown-menu>