[Tidy] Replace `dmc.Tooltip` with `dbc.Tooltip`

[huong-li-nguyen]

Description

• Replace dmc.Tooltip with dbc.Tooltip
• Remove all redundant CSS

@nadijagraca - I just double-checked and it seems like we can replace the dmc version with the dbc version now. Would you be so kind and finish this PR off? I've quickly tested it out for the tooltips in the NavLink and updated the CSS, but this still needs to be done:

• [x] Replace remaining dmc.Tooltip with dbc.Tooltip (in dashboard.py)
• [x] Remove all redundant CSS (double-check everything and remove variables, properties etc.)
• [x] Fix any CSS such that screenshots don't deviate (it should look more or less the same)
• [x] Update tests
• [x] Investigate warning @nadijagraca - Issue raised on dash bootstrap repo 1004
• [x] Replace screenshots where suitable @l0uden

Screenshot

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