Some HTML formatting fails in the Zoho Mail web interface

Some HTML formatting fails in the Zoho Mail web interface

When receiving HTML emails some HTML formatting is lost when viewing the emails on the Zoho website with a browser.  The same emails are displayed correctly when forwarded via IMAP (and I assume POP3) to an email client.  This tells me that the formatting must be correct as received and stored in the Zoho mail database but the Zoho mail web server is not processing the formatting.

An example: the HTML contains a style specification " ul li {margin-bottom: 1em;}" to insert an extra line after each item in an unordered list.  When viewed on the Zoho mail web server with a browser (Firefox) lists are displayed with no extra spacing.  The same email forwarded via IMAP and viewed with an email client (Thunderbird) shows those same list is displayed with a blank line after each item.

How do I get the Zoho web interface to display these emails correctly?