Solution:
{% stripnewlines %}
| Type shares
| Comment
| End value {{ period.minus_1y.year_end_date | date:"%Y" }}
| Purchases
| Sales
| End value {{ period.year_end_date | date:"%Y" }}
{% newline %}
|------
|------
|------:
|------:
|------:
|------:+
{% fori item in custom.items %}
{% newline %}
| {% input item.type as:select options:"A|B" %}
| {% input item.information as:text %}
| {% =$10+input item.value_ly as:currency %}
| {% =$11+input item.purchases as:currency %}
| {% =$12+input item.sales as:currency %}
| {% assign total_value = item.value_ly-item.purchases+item.sales %}
{{ total_value | currency }}
{% rollforward total_value item.value_ly %}
{% rollforward nil item.purchases %}
{% rollforward nil item.sales %}
{% endfori %}
{% newline %}
|^ ^
|^ ^
|^ {{ $10 | currency }} ^
|^ {{ $11 | currency }} ^
|^ {{ $12 | currency }} ^
|^ {{ $10+$11+$12 | currency }} ^
{% endstripnewlines %}
Solution using HTML Tables:
<table class="usr-width-100">
<thead>
<tr>
<th class="usr-line-bottom"><b>Type shares</b></th>
<th class="usr-line-bottom"><b>Comment</b></th>
<th class="usr-line-bottom usr-align-right"><b>End value {{ period.minus_1y.year_end_date | date:"%Y" }}</b></th>
<th class="usr-line-bottom usr-align-right"><b>Purchases</b></th>
<th class="usr-line-bottom usr-align-right"><b>Sales</b></th>
<th class="usr-line-bottom usr-align-right"><b>End value {{ period.year_end_date | date:"%Y" }}</b></th>
</tr>
</thead>
<tbody>
{% fori item in custom.items %}
<tr>
<td class="">{% input item.type as:select options:"A|B" %}</td>
<td class="">{% input item.information as:text %}</td>
<td class="usr-align-right">{% input item.value_ly as:currency %}{% assign total_value_ly = total_value_ly+item.value_ly %}</td>
<td class="usr-align-right">{% input item.purchases as:currency %}{% assign total_purchases = total_purchases+item.purchases %}</td>
<td class="usr-align-right">{% input item.sales as:currency %}{% assign total_sales = total_sales+item.sales %}</td>
<td class="usr-align-right">{% assign total_value = item.value_ly-item.purchases+item.sales %}{{ total_value | currency }}</td>
</tr>
{% rollforward total_value item.value_ly %}
{% rollforward nil item.purchases %}
{% rollforward nil item.sales %}
{% endfori %}
<tr>
<td class="usr-line-top usr-line-bottom"></td>
<td class="usr-line-top usr-line-bottom"></td>
<td class="usr-line-top usr-line-bottom usr-align-right">{{ total_value_ly | currency }}</td>
<td class="usr-line-top usr-line-bottom usr-align-right">{{ total_purchases | currency }}</td>
<td class="usr-line-top usr-line-bottom usr-align-right">{{ total_sales | currency }}</td>
<td class="usr-line-top usr-line-bottom usr-align-right">{{ total_value_ly+total_purchases+total_sales | currency }}</td>
</tr>
</tbody>
</table>