HTML example:

<div class="nk-widget">
    <h4 class="nk-widget-title">Search</h4>
    <div>
        <form action="" class="nk-form nk-form-style-1" novalidate="novalidate">
            <div class="input-group">
                <input type="text" class="form-control" placeholder="Type something...">
                <span class="nk-input-group-btn">
                    <button class="nk-btn nk-btn-color-dark-1"><span class="ion-search"></span></button>
                </span>
            </div>
        </form>
    </div>
</div>