Dropdown menu max height fix

[aGitForEveryone]

closes #2529
closes #2225

When a dash_table.DataTable is added to the dashboard (can be an empty table as well), css stylings are added to the Dash tool (see demonstration in #2529). These stylings override the max-height styling defined for the dropdown component, overriding the value set by the maxHeight property in dcc.Dropdown.

This fix changes the class names to which the css style is applied, so that the custom style set by Dropdown.css has higher priority than the dash_table.DataTable styling.

Contributor Checklist

• I have run the tests locally and they passed. (refer to testing section in contributing)
• I have added tests, or extended existing tests, to cover any new features or bugs fixed in this PR

optionals

• I have added entry in the CHANGELOG.md
• If this PR needs a follow-up in dash docs, community thread, I have mentioned the relevant URLS as follows
  • here is the show and tell thread in Plotly Dash community

[aGitForEveryone]

Thanks @ann-marie-ward for the help with setting up this PR (and creating the fix)

[T4rk1n]

💃 Looks good.