New rule: no-invalid-css

custom_types/csstree-validator.d.ts

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+declare module 'csstree-validator';

docs/rules/no-invalid-css.md

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+# Disallows invalid CSS in templates (no-invalid-css)
+
+Templates should all contain valid CSS, if any, as it is expected
+to be parsed as part of rendering.
+
+## Rule Details
+
+This rule disallows invalid CSS in templates.
+
+The following patterns are considered warnings:
+
+```ts
+css`foo bar`;
+css`.footer { 24px; color: blue; }`;
+```
+
+The following patterns are not warnings:
+
+```ts
+css`
+  .header {
+    margin: 24px;
+    color: blue;
+  }
+`;
+```
+
+## When Not To Use It
+
+If you don't care about invalid CSS, then you will not need this rule.