HTML and CSS Conflict with Joomla Code

I recently installed EShop on my Joomla 4.1.5 which is using the Shaper Helix Ultimate template 2.0.11. My articles have been written in html code with CSS styles included. After installing eshop, some of my html tags and css styles no longer apply, for example, the <ul><li></li></ul> tags for content in my articles.

Dear Marshall,

Thank you for submitting the ticket here. Please submit a new ticket to EShop category to send me the your site information so I can help you to check and resolve the issue for you.

Sincerely, Giang