In the past, the default formatting for slicers online was the same as for the desktop version. My team generates a slew of reports for our company and now all the slicers look different from how they look when we're building them. There used to be an underline beneath the title of each slicer and the title was larger and offset from the rest of the slicers; not only did this look better but it also made the slicers easier to read and easier to align on the page. It would be nice to have the old formatting restored.
If others are experiencing the same issue, vote for my idea here: https://ideas.powerbi.com/forums/265200-power-bi-ideas/suggestions/16303216-stop-reformatting-slicers-in-power-bi-online-kee