7 - Add classes to individual fields of paragraph bundle
Most people add another field, such as a select list with predefined options, and turn that into a class using a preprocess, or merge in the paragraph twig template.  If don't have a predefined list, and you allow user input, you will need to sanitize the input.

How I do it in the twig template is like this:

{# Renders Width field. #}
{# Sets class name from values in database. #}
{% if content.bp_width|render %}
  {% set layout_width = content.bp_width['#items'].getString() %}
  {% set layout_width_classes = [
'paragraph--width--tiny' == layout_width ? 'paragraph--width--tiny',
'paragraph--width--narrow' == layout_width ? 'paragraph--width--narrow',
'paragraph--width--medium' == layout_width ? 'paragraph--width--medium',
'paragraph--width--wide' == layout_width ? 'paragraph--width--wide',
'paragraph--width--full' == layout_width ? 'paragraph--width--full',
  ]
  %}
{% endif %}

{# The template default set classes. #}
{%
set classes = [
'paragraph',
'paragraph--type--' ~ paragraph.bundle|clean_class,
view_mode ? 'paragraph--view-mode--' ~ view_mode|clean_class,
]
%}

{# Merges Width field with classes. #}
{% set width_field = content.bp_width|render %}
{% if width_field %}
  {% set classes = classes|merge(layout_width_classes) %}
{% endif %}

{# Prints div with classes, and content without Width field. #}
&lt;div{{ attributes.addClass(classes) }}&gt;
  &lt;div class="paragraph__column"&gt;
    {{ content|without('bp_width') }}
  &lt;/div&gt;
&lt;/div&gt;


How do the Bootstrap styles get added?  Here is an excerpt from the LESS file:

.paragraph {
  .make-row();
  margin-left: 0;
  margin-right: 0;
}

.paragraph &gt; .paragraph__column {
  .make-sm-column(12);
  .make-md-column(12);
  .make-lg-column(12);
  padding-bottom: @jumbotron-padding;
}


Which compiles into the following CSS:

.paragraph {
  margin-left: -15px;
  margin-right: -15px;
  margin-left: 0;
  margin-right: 0;
}
.paragraph &gt; .paragraph__column {
  position: relative;
  min-height: 1px;
  padding-left: 15px;
  padding-right: 15px;
  padding-bottom: 30px;
}


You can overwrite that in your theme if needed.