fix (separator): prevent bottom separator overlapping content

[prconcepcion]

fixes #3061

[github-actions[bot]]

🤖 Pull request artifacts

file	commit
pr3081-stackable-3081-merge.zip	d207cd23945a7fc7db2ff2c3c8bded4636798ba6

[github-actions[bot]]

Try this Pull Request in the WordPress playground: https://playground.wordpress.net/?mode=seamless#{"landingPage":"/wp-admin/post-new.php?post_type=page","preferredVersions":{"php":"latest","wp":"latest"},"steps":[{"step":"login","username":"admin","password":"password"},{"step":"installPlugin","pluginZipFile":{"resource":"url","url":"https://raw.githubusercontent.com/gambitph/Stackable/artifacts/pr3081-stackable-3081-merge.zip"}}]}

[bfintal]

@prconcepcion Looks like this PR has issues with regards to background tints / gradients going above the separator. The changes from this PR have been reversed from the develop branch. Please create a new PR with the adjusted fix