clr-angular-static-fix/layout/vertical-nav/vertical-nav.html

1. Install Clarity Icons package through npm:

<!--
  ~ Copyright (c) 2016-2018 VMware, Inc. All Rights Reserved.
  ~ This software is released under MIT license.
  ~ The full license information can be found in LICENSE in the root directory of this project.
  -->

<button type="button" class="nav-trigger"
        [class.on-collapse]="collapsed"
        (click)="toggleByButton()"
        *ngIf="collapsible">
    <clr-icon shape="angle-double" class="nav-trigger-icon" [attr.dir]="(this.collapsed) ? 'right' : 'left'"></clr-icon>
</button>
<!-- Click handler on .nav-content is bad but required :-( -->
<div class="nav-content">
    <ng-content></ng-content>
    <button (click)="collapsed = false" class="nav-btn" *ngIf="collapsible && collapsed"></button>
</div>