fix(deps): upgrade default template to Bootstrap 5.3.8

[vicancy]

Summary

• Upgrade the default template from Bootstrap 3.4.1 to 5.3.8 because the affected Bootstrap 3 advisories have no patched 3.x release.
• Upgrade twbs-pagination 1.3.1 → 1.4.2 for Bootstrap 5 page-item and page-link markup while retaining the existing search flow.
• Migrate default and statictoc navbar, dropdown, breadcrumb, TOC, collapse, alert-icon, filtering, and article-navigation behavior to Bootstrap 5 APIs and classes.
• Adopt native Bootstrap 5 presentation rather than recreating Bootstrap 3: 16px body text, 40px H1, underlined content links, Bootstrap 5 container widths/gutters, regular table spacing, and unstyled blockquotes are intentional.
• Keep only functional layout safeguards: measured fixed-header offsets, footer clearance, overflow-driven navbar collapse, mobile TOC/dropdown behavior, and robust anchors for dynamic, numeric, dotted, and Unicode heading IDs.
• Leave all unrelated npm packages, NuGet packages, GitHub Actions, and Dependabot policy unchanged.

⚠️ Breaking changes for custom templates

This is an intentional breaking change for custom templates layered on default or statictoc. Docfx merges templates by file name, with later templates replacing earlier files in full. A custom template that overrides an old Bootstrap 3 partial, stylesheet, or script can therefore combine Bootstrap 3 markup with Bootstrap 5 assets and lose navbar, dropdown, collapse, TOC, or affix behavior.

Custom templates need migration if they override files such as:

• layout/_master.tmpl
• partials/navbar.tmpl.partial
• partials/toc.tmpl.partial
• partials/li.tmpl.partial or dropdown partials
• styles/docfx.css
• styles/docfx.js

Common Bootstrap 3 → 5 replacements include:

Bootstrap 3	Bootstrap 5
data-toggle	data-bs-toggle
data-target	data-bs-target
.collapse.in	.collapse.show
.navbar-toggle	.navbar-toggler
.navbar-inverse	.navbar-dark.bg-dark
.pull-right	.float-end
.hidden-* / .visible-*	responsive .d-* utilities
.table-condensed	.table-sm
Glyphicons	Bootstrap Icons or another icon source

Bootstrap 5 no longer exposes Bootstrap components as jQuery plugins. Custom JavaScript using calls such as $(...).collapse(), $(...).tab(), or $(...).dropdown() must use the Bootstrap 5 APIs. Bootstrap 3 affix and scrollspy assumptions also require migration.

Visual assumptions may change because this PR adopts Bootstrap 5 typography, link decoration, table spacing, responsive containers, gutters, breakpoints, blockquotes, navbar, breadcrumbs, and pagination.

Custom templates that are fully standalone, or that only override tokens/localization, preprocessors, data-model extensions, or CSS/JavaScript that does not depend on Bootstrap markup, are not expected to require migration.

Before upgrading, run docfx template export default and reconcile any overridden files with the new Bootstrap 5 versions. This change should be called out in release notes and is best reviewed for a prerelease or explicitly breaking release.

Bootstrap 5 preview

Video walkthrough

35-second walkthrough covering desktop styling, Markdown/tables, tabs, Bootstrap components, search/pagination, footer clearance, and mobile navbar/TOC:

bootstrap5-migration-demo.mp4

Screenshots

Expanded screenshots

Native Bootstrap 5 content styling

Bootstrap components

Mobile navigation

Footer clearance

Validation

• Default and statictoc builds complete with warnings treated as errors.
• Native Bootstrap 5 metrics verified: 16px body, 40px H1, underlined links, 8px table cells, and 540/720/960/1140/1320px responsive containers.
• Header and footer bounds verified with zero content overlap; mobile footer detection uses the visual viewport.
• Navbar overflow/collapse, dropdowns, mobile TOC, TOC filtering, tabs, dynamic refresh, numeric/dotted/Unicode anchors, search, and pagination exercised in-browser.
• Full multi-target .NET warning-as-error build, formatting verification, cross-platform CI, and Percy visual review.