bootstrap-tables2.css

.table-container th.asc:after {
  content: '\0000a0\0025b2';
}
.table-container th.desc:after {
  content: '\0000a0\0025bc';
}
.pagination {
  text-align: center;
}

table.html

{% load querystring from django_tables2 %}
{% load trans blocktrans from i18n %}
{% load bootstrap3 %}
 
{% if table.page %}
<div class="table-container">
{% endif %}
 
{% block table %}
<table class="table table-striped"{% if table.attrs %} {{ table.attrs.as_html }}{% endif %}>
    {% block table.thead %}
    <thead>
        <tr>
        {% for column in table.columns %}
            {% if column.orderable %}
            <th {{ column.attrs.th.as_html }}><a href="{% querystring table.prefixed_order_by_field=column.order_by_alias.next %}">{{ column.header }}</a></th>
            {% else %}
            <th {{ column.attrs.th.as_html }}>{{ column.header }}</th>
            {% endif %}
        {% endfor %}
        </tr>
    </thead>
    {% endblock table.thead %}
    {% block table.tbody %}
    <tbody>
        {% for row in table.page.object_list|default:table.rows %} {# support pagination #}
        {% block table.tbody.row %}
        <tr class="{% cycle "odd" "even" %}">
            {% for column, cell in row.items %}
                <td {{ column.attrs.td.as_html }}>{{ cell }}</td>
            {% endfor %}
        </tr>
        {% endblock table.tbody.row %}
        {% empty %}
        {% if table.empty_text %}
        {% block table.tbody.empty_text %}
        <tr><td colspan="{{ table.columns|length }}">{{ table.empty_text }}</td></tr>
        {% endblock table.tbody.empty_text %}
        {% endif %}
        {% endfor %}
    </tbody>
    {% endblock table.tbody %}
    {% block table.tfoot %}
    <tfoot></tfoot>
    {% endblock table.tfoot %}
</table>
{% endblock table %}
 
{% if table.page %}
    {% block pagination %}
        {% bootstrap_pagination table.page %}
    {% endblock pagination %}
{% endif %}

Looks like with
<table class="table table-striped"{% if table.attrs %} {{ table.attrs.as_html }}{% endif %}> we can't apply customized attrs in class Meta.
So I just changed it back to the original one:
<table{% if table.attrs %} {{ table.attrs.as_html }}{% endif %}>
Then I need to give full class values to attrs in class Meta, for example: attrs = {'class': 'table table-striped table-boardered table-hover'}