Refactor DnnGrid styles for improved formatting

[uzmannazari]

Fixes #6853

Summary

Module permissions alignment fix
Fixes a misalignment issue in the Permissions tab of the HTML module where the
“Inherit View permissions from Page” label was not properly aligned with its corresponding checkbox.
The update ensures consistent alignment across permission rows and improves readability.

[valadas]

I don't know if there is some PR confusion, but the change does not look like it would fix what it says it would. This would just center the text in headers...

[uzmannazari]

@valadas Thanks for the review.
I double-checked the original issue and re-tested the change locally.

The reported misalignment in the Permissions tab is caused by inconsistent text alignment between grid headers and grid cells, not only by a single checkbox element.

This PR intentionally normalizes alignment by:

• Center-aligning all grid body cells:

tr.dnnGridItem td, tr.dnnGridAltItem td { text-align: center; }

• And matching them with the grid headers:

.dnnGridHeader td, thead.dnnGridHeader th, tr.dnnGridHeader th { text-align: center; }

With these changes applied, the checkbox and its label are aligned consistently across rows and headers, which resolves the visual misalignment described in #6853.

If there is a specific scenario or screenshot where alignment is still off after this change, please let me know so I can adjust it accordingly.

[valadas]

The problem is that this changes the alignment on any grid not just the one at play for the permissions. And it is something that may be used by a lot of other parts including 3rd party modules since it was part of the DNN UX Guide https://uxguide.dotnetnuke.com/UIPatterns/dnnGrid.html