<h4>Basic buttons</h4>
<button type="button" class="btn btn-primary">Primary</button>
<button type="button" class="btn btn-secondary">Secondary</button>
<button type="button" class="btn btn-link">link</button>

<hr>

<h4>Outline buttons</h4>
<button type="button" class="btn btn-outline-primary">Primary</button>
<button type="button" class="btn btn-outline-secondary">Secondary</button>

<hr>

<h4>Button sizes</h4>
<button type="button" class="btn btn-primary btn-lg">Large button</button>
<button type="button" class="btn btn-primary">Normal button</button>
<button type="button" class="btn btn-primary btn-sm">Small button</button>
<br><br>
<button type="button" class="btn btn-outline-secondary btn-lg">Large outline button</button>
<button type="button" class="btn btn-outline-secondary">Medium outline button</button>
<button type="button" class="btn btn-outline-secondary btn-sm">Small outline button</button>

<hr>

<h4>Button block level</h4>
<button type="button" class="btn btn-primary btn-lg btn-block">Large block level button</button>
<br>
<button type="button" class="btn btn-outline-secondary btn-block">Medium secondary outline button</button>
<h4>Basic buttons</h4>
{% render '@button' %}
{% render '@button--secondary' %}
{% render '@button--link' %}

<hr>

<h4>Outline buttons</h4>
{% render '@button-outline--primary' %}
{% render '@button-outline--secondary' %}

<hr>

<h4>Button sizes</h4>
{% render '@button-size--large' %}
{% render '@button-size--normal' %}
{% render '@button-size--small' %}
<br><br>
{% render '@button', {class:'btn-outline-secondary btn-lg', text:'Large outline button'} %}
{% render '@button', {class:'btn-outline-secondary', text:'Medium outline button'} %}
{% render '@button', {class:'btn-outline-secondary btn-sm', text:'Small outline button'} %}

<hr>

<h4>Button block level</h4>
{% render '@button-size--large-block' %}
<br>
{% render '@button', {class:'btn-outline-secondary btn-block', text:'Medium secondary outline button'} %}
/* No context defined for this component. */

Just overview of almost all button combinations.