Version pinning versus CSS custom properties for safe Bulma upgrades with legacy browser constraint

Answer

Version pinning provides the documented rollback path for recovering from a failed Bulma upgrade without changing HTML markup. CSS custom properties (introduced in Bulma 0.9.0) do not replace the need to pin the core version for visual stability, and they only add runtime theming on top of the pinned CSS when the browser supports them.

Confirmed facts

• Pinning Bulma to an exact version in package.json, lockfile, or a fixed CDN URL lets you reinstall that version to revert any upstream visual change.
• Bulma ≥ 0.9.0 ships CSS custom properties (e.g., --primary) that can be overridden at runtime via :root; this does not undo layout, spacing, or selector changes made in a new release.
• Legacy browsers that lack CSS custom property support ignore runtime overrides and use the shipped CSS as‑is.
• When both a pinned version and custom‑property overrides are present, the pinned CSS forms the base; overrides apply only if the pinned version includes the properties and the browser supports them; otherwise the base styles remain unchanged.

Steps for this case

1. Pin Bulma to a known good version (e.g., "bulma": "0.8.0") in your dependency manager or use a versioned CDN URL like https://cdn.jsdelivr.net/npm/bulma@0.8.0/css/bulma.min.css.
2. Deploy the application; if an upstream upgrade breaks appearance, revert by reinstalling the pinned version or switching the CDN back to the previous version URL.
3. If you need runtime theming and the target browsers support CSS custom properties, add a :root block with your variable overrides after the Bulma stylesheet.
4. Test the page in the legacy browsers to confirm that custom‑property overrides are ignored and the pinned base styles render as expected.

Missing diagnostic detail: Please confirm whether the specific legacy browsers you must support lack CSS custom property support. If they do support them, the custom‑property theming approach can be used alongside pinning, but pinning remains required for visual stability.