I suggest taking a look at your html sanitization settings make sure html isn't allowed in markdown settings.
Next step would be to move the other 2 topics from that category and check if you still see broken markup.
You can disable it here: https://github.com/designcreateplay/nodebb-theme-lavender/blob/master/static/lib/lavender.js#L42
Not sure about changing the width to 100%, you'd have to ask @baris
Haha totally missed that, was looking in the LESS