<style>
 table.calendar > * {
     font-family: sans;
 }

 table.calendar {
     width: 100%;
     border-collapse: collapse;
 }

 tr.month > td {
     text-align: center;
     font-weight: bold;
     border-bottom: 2px solid black;
     padding-bottom: .5em;
 }

 tr.days > td {
     text-align: center;
     border-bottom: 2px solid black;
 }

 tr.week > td {
     height: 3em;
 }

 tr.week > td > span.day-num {
     font-weight: bold;
 }

 tr.week > td.other-month > span.day-num {
     font-weight: normal;
     color: #909090;
 }

 tr.week > td.today {
     background-color: #d8d8d8;
 }

 td > div.event {
     border: 1px solid green;
     background-color: white;
     border-radius: 2px;
 }
</style>
<table class="calendar">
    <thead>
        <tr class="month">
            <td colspan="7">{{ calendar.month }}</td>
        </tr>
        <tr class="days">
{% for day in calendar.day_names %}
            <td>
                {{ day }}
            </td>
{% endfor %}
        </tr>
    </thead>
    <tbody>
{% set markers = namespace() -%}
{% set markers.first = true -%}
{% for day in calendar.days -%}
    {% if loop.index0 % (calendar.day_names) | length == 0 -%}
        {% if not markers.first %}
        </tr>
        {%- else %}
            {%- set markers.first = false %}
        {%- endif %}
        <tr class="week">
    {%- endif %}
            <td class="{% if day.month != calendar.timestamp.month %} other-month{% endif %}{% if day.date() == calendar.timestamp.date() %} today{% endif %}">
                <span class="day-num">{{ day.day }}</span>
    {% if day.date() == calendar.timestamp.date() %}
                <div class="event">
                    This is a task
                </div>
    {% endif %}
            </td>
{% endfor %}
        </tr>
    </tbody>
</table>