Content-Security-Policy

UnoCSS is great until you turn on a strict Content Security Policy and your styling quietly falls apart. That’s the tradeoff with on-demand atomic CSS. UnoCSS can inject styles at runtime, and CSP tends to hate runtime injection unless you explicitly allow it. If you’ve ever tightened style-src and then watched your app render as unstyled HTML, you’ve already met the problem. The short version: if UnoCSS is generating or injecting <style> tags in the browser, you need to account for that in CSP. If you can shift style generation to build time or server render time, life gets much easier. ...

Adobe Fonts is one of those integrations that looks trivial until your CSP starts blocking it in production. You add the embed code, ship a strict policy, and suddenly your typography falls back to system fonts. Or worse, you loosen style-src too much just to get it working and quietly undo a big chunk of your CSP hardening. I’ve had to clean this up more than once. The good news: Adobe Fonts usually needs only a small set of allowances. The bad news: a lot of examples online are either too broad or copy-pasted from unrelated setups. ...

Vanilla Extract is one of the easier styling tools to live with under a strict Content Security Policy. That’s the good news. The reason is simple: Vanilla Extract compiles styles to real CSS files at build time. No runtime style injection, no CSS-in-JS engine pushing <style> tags into the DOM on page load, no constant fight with style-src nonces. If you care about CSP, that’s already a huge win. Still, “works better with CSP” is not the same thing as “done.” Teams often ship a decent script-src and then quietly leave style-src 'unsafe-inline' hanging around forever because some analytics tool, consent manager, or framework edge case made it convenient. ...

SoundCloud embeds look simple: paste an <iframe>, ship it, done. Then CSP gets involved and the player disappears, the console fills with violations, and somebody “fixes” it by slapping https: into half the policy. That’s the usual failure mode. If you’re embedding SoundCloud on a site with a real Content Security Policy, the trick is to allow exactly what the embed needs and nothing else. Most breakages come from guessing the wrong directive, overusing default-src, or trying to force a third-party widget into a policy designed only for first-party code. ...

goober is tiny, fast, and refreshingly unpretentious. That’s exactly why people like it. But the moment you try to lock down a real app with Content Security Policy, CSS-in-JS stops being a styling choice and starts becoming a security deployment problem. The short version: goober usually injects styles into <style> tags at runtime. CSP cares a lot about that. If your policy is strict, those injected styles can get blocked unless you deliberately allow them. ...

Chart.js v4 is one of the easier charting libraries to run under a strict Content Security Policy. That’s the good news. The less fun part: “easier” does not mean “automatic.” The moment you mix Chart.js with inline bootstrapping code, third-party plugins, CDN delivery, tag managers, or framework hydration tricks, your policy gets messy fast. I’ve had to clean this up more than once, and the pattern is always the same: the chart library itself is usually fine, but the surrounding app code quietly punches holes in CSP. ...

Sass + CSS Modules usually feels boring in the best possible way. You write .module.scss, import it into a component, get locally scoped class names, and move on with your life. Then CSP shows up and breaks your build in ways that are annoyingly indirect. The tricky part is that Sass CSS Modules themselves are not the problem. The problem is how your toolchain delivers the compiled CSS to the browser. Some setups emit static .css files. Others inject <style> tags at runtime. CSP treats those very differently. ...

A lot of CSP breakage looks random until you hit icons. Text loads. JavaScript loads. Layout mostly works. Then half the UI shows empty squares, missing chevrons, or buttons with no visual affordance at all. I’ve seen teams burn hours blaming CSS pipelines when the real problem was much simpler: the icon delivery method didn’t match the site’s Content Security Policy. This case study is about that exact problem with Evergreen icons on a production-style setup. ...

Embedding Apple Music looks simple right up until your CSP blocks it and leaves you staring at a blank iframe. I’ve hit this a few times on locked-down sites: the page loads fine, your own scripts work, and then the Apple Music player silently fails because frame-src or child-src doesn’t allow Apple’s embed origin. If you’re running a reasonably strict policy, you need to account for the iframe itself and, depending on your setup, any assets or network requests your page makes around it. ...

Highlight.js is usually easy to lock down with Content Security Policy. The core library does not need eval, it does not need inline event handlers, and it works fine under a strict policy if you load it like a normal script. The place where people get sloppy is theming. They drop in inline <style> blocks, use broad CDN allowlists, or keep style-src 'unsafe-inline' around because syntax highlighting “needs it”. It doesn’t. ...