You need to generate data source from your hierarchy to be something like this
@toc = [ ['header', 0], ['subheader', 1], ['subsubheader', 2],
['header2', 0], ['header3', 0], ['subheader2', 1]
]
Than it is easy to render it in template, for example:
<%- @toc.each do |item, distance| %>
<%= (' ' * distance * 5).html_safe %>
<%= item %>
<br/>
<%- end %>
Would give you:
header
subheader
subsubheader
header2
header3
subheader2
Of course you can use 'distance' for determining style size instead of 'depth', but I hope you get the main idea.