getSegment matching category title
You might do something like this, concerned that you want to set current on active category.

{% set categorySlug = craft.request.getLastSegment() %} 

{% nav category in craft.categories.group('blogCategories') %}
    {% set current = (category.slug == categorySlug) %}
    &lt;a class="button button--outline-blue 
       {% if current %} current{% endif %}
       href="{{ category.url }}"&gt;
       {{ category.title }}
    &lt;/a&gt;
{% endnav %}