Fixes the sidebar margin top

[Godmartinz]

Description

Adjusts the sidbar menu's top margin so that it clears the nav header and all buttons are clickable for all media sizes.

Fixes #12571

Type of change

Please delete options that are not relevant.

• [ x] Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

• Test A
• Test B

Test Configuration:

• PHP version:
• MySQL version
• Webserver version
• OS version

Checklist:

• I have read the Contributing documentation available here: https://snipe-it.readme.io/docs/contributing-overview
• I have formatted this PR according to the project guidelines: https://snipe-it.readme.io/docs/contributing-overview#pull-request-guidelines
• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[what-the-diff]

• The margin-top of the sidebar menu was changed for different screen sizes.
• For screens smaller than 512px, it is now 160px instead of 64px.
• For screens between 772 and 1098 pixels wide, it is 98 px instead of 51 px (the original value).

[snipe]

That seems like too much of a margin tho? Dashboard should fit cleanly under the hamburger, IMHO