Misleading indentation of some TOC entries

[diego-plan9]

Some items/levels in the TOC are shown with the wrong indentation, hindering readability - for example:

In the screenshot, the Terra organization entry is visually at the same level as Overview, but the real hierarchy is:

Qiskit Terra
    Overview
        Terra Organization
    The Quantum Circuit
    ...

Pinging @Borjagodoy - can you double check the relevant parts of the theme for the TOC? Please note that there might be other oddities potentially related, such as the indentation for an "entry that has subentries" vs the intentation for an "entry that has no subentries".

Also, it seems the original theme already had the collapsing/expanding functionality baked in by default (on the sample site, with some circles around the arrows and no extra changes) - can you evaluate if we can reuse it directly, instead of tuning the html and CSS?

[diego-plan9]

Following up on the last bit of the comment, currently there are two <div class="globaltoc"> entries, which might be related. Since each one takes up ~40kb (and we end up producing ~400 files), can we also look into removing this duplicity, as it is also causing some minor issues in non-javascript enabled browsers?