I can't guarantee this is perfect and won't break anything so be backed up or test in anew style
In your style template
node_list_category
cut this out:
Code:
<h2 class="block-header">
<a href="{{ link('categories', $node) }}">{$node.title}</a>
<xf:if is="{$node.description}"><span class="block-desc">{$node.description|raw}</span></xf:if>
</h2>
And paste back above line 4
<div class="block-container">
(Currently the header is inside the container, you want it above the container)
Then add a bottom margin in extra.less
Code:
h2.block-header
{
margin-bottom:10px;
}