Set zebra-style (odd/even) classes in twig loop in drupal 8 (bootstrap) theme
<div{{ attributes.addClass('container') }}>
{% for item in items %}
{# NB! notation: loop.index is 1 start, loop.index0 is zero start #}
<div class="row {{ loop.index0 is odd ? 'zebra-odd' : 'zebra-even' }}">
<div{{ item.attributes }}>{{ item.content }}</div>
</div>
{% endfor %}
</div>