I had a client last week—a large scale e-commerce shop—practically screaming because their carefully crafted H2 styles were being mangled inside the Block Editor. On the frontend, everything looked crisp. In the backend? Total disaster. It’s a classic specificity war where core block styles start bullying your theme’s CSS, and it’s enough to make any senior dev want to throw their keyboard through a window.
My first instinct, years ago, would have been to just slap an !important on every heading class and call it a day. Trust me, I’ve been there. But we all know how that ends: you spend the next six months playing whack-a-mole with CSS overrides until your stylesheet is 5,000 lines of regret. Then I tried getting clever with highly specific selectors, targeting nested containers in the editor. That worked until the next minor WordPress update shifted the DOM structure. Not good. The real fix needed to come from the core level.
Why the WordPress 6.9 CSS Specificity Fix is a Big Deal
According to the latest Dev Chat Agenda, WordPress 6.9 is tackling this head-on. The upcoming release, currently at Release Candidate 3, includes a specific Heading Block CSS specificity fix that finally addresses these styling conflicts. It’s part of a broader effort to make the editor experience actually match what the user sees on the site without requiring developers to write “hacky” CSS.
In the past, core styles often had a higher specificity than theme-provided styles in certain contexts, especially when using theme.json. With 6.9, they’re refining how these styles are injected. This means your bbioon_custom_heading_styles will actually behave as expected. Here is a look at how we’re starting to structure our theme overrides now that the specificity is becoming more predictable:
// Simplified theme.json approach for 6.9
{
"version": 3,
"settings": {
"blocks": {
"core/heading": {
"typography": {
"fontWeight": "700",
"lineHeight": "1.2"
}
}
}
},
"styles": {
"blocks": {
"core/heading": {
"css": "padding-bottom: 0.5rem; border-bottom: 2px solid var(--wp--preset--color--primary);"
}
}
}
}Beyond the CSS fixes, 6.9 is packing some serious heat with the Interactivity API and DataViews. If you haven’t looked into DataViews yet, you’re in for a treat—or a headache, depending on how much custom admin work you do. They are moving more of the admin interface toward a data-driven model, which is great for performance but means we all have to learn a few new patterns. I’m already looking at how we can use the new Abilities API to tighten up client-side permissions for some of our more complex WooCommerce builds.
Preparing for the December 2nd Launch
WordPress 6.9 is slated for December 2, 2025. If you haven’t grabbed RC3 to test your current projects, you’re playing with fire. One of the topics brought up in the Dev Chat was the distinction between browser support for the admin core versus the frontend. This is a subtle point, but it matters for those of us supporting clients on legacy corporate infrastructure. Making sure your frontend output remains compatible while the backend leverages modern APIs is a balancing act we perform daily.
Look, this stuff gets complicated fast. Between the specificity changes and the new iframe integration for the post editor, there are plenty of places for things to break. If you’re tired of debugging someone else’s mess and just want your site to work through the next major update, drop my team a line. We’ve probably seen it before and already have a fix ready.
The lesson here? Stop fighting the editor with CSS hacks. Use the tools core is giving us. It’ll save you a lot of gray hair in the long run. Trust me on this one.
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