how to add class in drop down menu and set the dorp down menu with out using module in drupal 8

Step 1:-  Goto + Configure block + click

Step 2:-  Goto + Menu levels + click to check box Expand all menu items

Like

 

And save

Step 3:-  I have A Hmtl

Step 4:- Add the class in twig file

We have a twig file 

Menu.html.twig

Step 5: override the twig file and add the class of the file 

Code:-

{% import _self as menus %}

{#

  We call a macro which calls itself to render the full tree.

  @see http://twig.sensiolabs.org/doc/tags/macro.html

#}

{{ menus.menu_links(items, attributes, 0) }}

{% macro menu_links(items, attributes, menu_level) %}

  {% import _self as menus %}

  {% if items %}

    {% if menu_level == 0 %}

      <ul{{ attributes.addClass('menu', 'nav', 'navbar-nav') }}>

    {% else %}

      <ul{{ attributes.addClass('dropdown-menu') }}>

    {% endif %}

    {% for item in items %}

      {% if menu_level == 0 and item.is_expanded %}

        <li{{ item.attributes.addClass('expanded', 'dropdown') }}>

        <a href="{{ item.url }}" class="dropdown-toggle" data-target="#" data-toggle="dropdown">{{ item.title }} <span class="caret"></span></a>

      {% else %}

        <li{{ item.attributes }}>

        {{ link(item.title, item.url) }}

      {% endif %}

      {% if item.below %}

        {{ menus.menu_links(item.below, attributes.removeClass('nav', 'navbar-nav'), menu_level + 1) }}

      {% endif %}

      </li>

    {% endfor %}

    </ul>

  {% endif %}

{% endmacro %}