feat(aio): add aio-select component

Provide the functionality for select menus in a single reusable component.

aio/src/styles/2-modules/_modules-dir.scss

@@ -27,3 +27,4 @@
    @import 'search-results';
    @import 'subsection';
    @import 'toc';
+   @import 'select-menu';

aio/src/styles/2-modules/_select-menu.scss

@@ -0,0 +1,72 @@
+/* SELECT MENU */
+
+.form-select-menu {
+  position: relative;
+}
+
+.form-select-button {
+  background: $white;
+  box-shadow: 0 2px 2px rgba($black, 0.24), 0 0 2px rgba($black, 0.12);
+  box-sizing: border-box;
+  border: 1px solid $white;
+  color: $blue-grey-600;
+  font-size: 12px;
+  font-weight: 400;
+  height: 32px;
+  line-height: 32px;
+  outline: none;
+  padding: 0 16px;
+  text-align: left;
+  width: 100%;
+  cursor: pointer;
+
+  strong {
+    font-weight: 600;
+    margin-right: 8px;
+    text-transform: uppercase;
+  }
+
+  &:focus {
+    border: 1px solid $blue-400;
+    box-shadow: 0 2px 2px rgba($blue-400, 0.24), 0 0 2px rgba($blue-400, 0.12);
+  }
+}
+
+.form-select-dropdown {
+  background: $white;
+  box-shadow: 0 16px 16px rgba($black, 0.24), 0 0 16px rgba($black, 0.12);
+  border-radius: 4px;
+  list-style-type: none;
+  margin: 0;
+  padding: 0;
+  position: absolute;
+  top: 0;
+  width: 100%;
+  z-index: $layer-2;
+
+  li {
+    cursor: pointer;
+    font-size: 14px;
+    line-height: 32px;
+    margin: 0;
+    padding: 0 16px 0 40px;
+    position: relative;
+    transition: all .2s;
+
+    &:hover {
+      background: $blue-grey-50;
+      color: $blue-500;
+    }
+
+    &.selected {
+      background-color: $blue-grey-100;
+    }
+
+    .symbol {
+      left: 16px;
+      position: absolute;
+      top: 8px;
+      z-index: $layer-5;
+    }
+  }
+}