Resolve #3457688 "Support for core"

Closes #3457688

css/environment_indicator-navigation.css

+/* Active environment button background and font colors. */
+.admin-toolbar .toolbar-button.toolbar-button--environment-indicator,
+.admin-toolbar .toolbar-button.toolbar-button--environment-indicator-label {
+  color: var(--env-indicator-fg-color);
+  background-color: var(--env-indicator-bg-color);
+}
+
+[data-admin-toolbar="expanded"] .toolbar-button.toolbar-button--environment-indicator {
+  padding-inline-start: var(--admin-toolbar-space-16);
+}
+
+[data-admin-toolbar="expanded"] .toolbar-button.toolbar-button--environment-indicator::before {
+  display: none;
+}