website/_includes/search-docs.html

<div class="col-md-3{% unless page.mobile_search or layout.mobile_search %} hidden-sm-down{% endunless %}">
  <div class="search">
    <label class="search-label sr-only" for="algolia-doc-search">
      Search docs
    </label>

    {% include svg/icon-search.svg %}

    <input type="search"
      class="search-input form-control"
      id="algolia-doc-search"
      placeholder="Search docs"/>
  </div>
</div>