Add layout width option

[fenbox]

Is your enhancement request related to a problem? Please describe

Always the widest, when used as a platform under a website, visually causes an insufficiently harmonious change in width.

Describe the solution you'd like

Add an option to control the maximum width on both sides.

Full-width: Default, i.e., the current width, the sidebar navigation is always flush with the left edge.

Fixed-width: Maximum width of xxl.