drawer is not properly calculating its size when --nuxeo-app-top is defined

When we set a height to --nuxeo-app-top our interface is breaking in a couple of places:

• administration icons are not visible because they are pushed to the bottom;
• the last item of tasks drawer list is pushed to the bottom.

We can reproduce this bug by setting, for example, --nuxeo-app-top to 100px, in our theme.html.