Update from code changes: Document sidebar and content width CSS variables

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Summary

Sites can now resize the desktop layout with two CSS variables. --sidebar-width sets the sidebar width, and the content area, header, and footer adjust to match. --content-width sets the maximum width of the text column on default-mode pages. When neither variable is set, every theme looks the same as before.

Changes

• Added a "Change the sidebar width" section to the custom CSS page. It includes an example and a table of each theme's default width.
• Noted that in Palm the variable only sets the expanded sidebar's width.
• Added a "Change the content width" section. It includes an example and a table of each theme's default width. It also notes that the column stops at the space beside the sidebar and table of contents, and that wide, center, custom, and frame modes are unaffected.

Update history

• Documented the --sidebar-width CSS variable.
• Documented the --content-width CSS variable.

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Note

Low Risk
Documentation-only updates to the custom CSS page; no runtime or product code changes.

Overview
Extends Custom scripts with two CSS customization guides on customize/custom-scripts.mdx.

Change the sidebar width documents --sidebar-width for desktop: layout (content, header, footer) follows the variable so sites need not hand-tune #sidebar. It includes a :root example, per-theme default widths, and a Palm note that only the expanded sidebar respects the variable.

Change the content width documents --content-width for the default page mode text column max width, with behavior when space is limited, theme default table, and an explicit exclusion for wide, center, custom, and frame page modes.

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Update from code changes updated this PR.

Added content width section showing --content-width usage and theme defaults

Source PRs

• mintlify/mint#12450 — feat(client): add --content-width CSS variable