solr reverse proxy Apache2

The links from the HTML content page for the CSS and other files are probably absolute paths - so they're linked to /solr/path/to/css instead of path/to/css.

You should be able to solve this by adding another ProxyPass:

ProxyPass /solrsearch http://localhost:8983/solr/collection1/browse
ProxyPassReverse /solrsearch http://localhost:8983/solr/collection1/browse
ProxyPass /solr http://localhost:8983/solr

But, you should be careful that that's not exposing more content than you want exposed if this is a publicly available server.

just to tag on here. The following proxy configuration permits the default Solr browser to operate (with CSS, javascript, etc) without giving access to the admin functions:

<IfModule mod_proxy.c>
    # Proxy specific settings
    ProxyRequests Off

    <Proxy *>
        AddDefaultCharset off
        Order deny,allow
        Allow from all
    </Proxy>

    # permit:
    #  * queries
    #  * javascript
    #  * css
    #  * term vectors
    # restrict:
    #  * all other traffic (admin, etc)

    ProxyPassMatch "/solr/(.*/browse)" http://localhost:8983/solr/$1
    ProxyPassMatch "/solr/(.*/terms)" http://localhost:8983/solr/$1
    ProxyPassMatch "/solr/(.*/admin/file)" http://localhost:8983/solr/$1
    ProxyPass /solr/js http://localhost:8983/solr/js
    ProxyPassReverse /solr http://localhost:8983/solr
</IfModule>

This is working on my Solr 6.1.0 system.