# UNSAFE_RUNTIME_CSS: CSS built at run time

> CSS built at run time

| Severity | Fault                         | Stage        |
| -------- | ----------------------------- | ------------ |
| error    | customer (the source package) | build output |

## What it means

The component creates a <style> element, a CSSStyleSheet or calls insertRule or replaceSync, so its CSS is made at run time. The build checks the component's CSS for @import, network url() and declared parts and variables; CSS made at run time skips those checks, and a <style> element needs the host page's style-src (rule runtime-css).

## How to fix

Put the CSS in a .css or .scss file the component imports, or in defineTaggorComponent({ styles }); for values that change, set a CSS variable in a style prop.