views/macros/button_classes.html.twig
{% macro button_classes(color, size, type, extra) %}
{% if color == 'info' %}
button-secondary
{% else %}
button-{{ color }}
{% endif %}
{% if size == 'extra-small' %}button-xsmall{% endif %}
{% if size == 'small' %}button-small{% endif %}
{% if size == 'medium' %}{# No need for an extra class #}{% endif %}
{% if size == 'large' %}button-large{% endif %}
{% if size == 'extra-large' %}button-xlarge{% endif %}
{{ type }}
{{ extra }}
{% endmacro %}