Merge commit '9b0050e9aabe4be65c78ccf292a348f309d50ccd' as 'docs'

```
git subtree add --prefix=docs/ https://github.com/gohugoio/hugoDocs.git master --squash
```

Closes #11925

docs/content/en/functions/safe/CSS.md

@@ -0,0 +1,33 @@
+---
+title: safe.CSS
+description: Declares the given string as safe CSS string.
+categories: []
+keywords: []
+action:
+  aliases: [safeCSS]
+  related:
+    - functions/safe/HTML
+    - functions/safe/HTMLAttr
+    - functions/safe/JS
+    - functions/safe/JSStr
+    - functions/safe/URL
+  returnType: template.CSS
+  signatures: [safe.CSS INPUT]
+aliases: [/functions/safecss]
+---
+
+In this context, *safe* means CSS content that matches any of the following:
+
+1. The CSS3 stylesheet production, such as `p { color: purple }`.
+2. The CSS3 rule production, such as `a[href=~"https:"].foo#bar`.
+3. CSS3 declaration productions, such as `color: red; margin: 2px`.
+4. The CSS3 value production, such as `rgba(0, 0, 255, 127)`.
+
+Example: Given `style = "color: red;"` defined in the front matter of your `.md` file:
+
+* `<p style="{{ .Params.style | safeCSS }}">…</p>` &rarr; `<p style="color: red;">…</p>`
+* `<p style="{{ .Params.style }}">…</p>` &rarr; `<p style="ZgotmplZ">…</p>`
+
+{{% note %}}
+`ZgotmplZ` is a special value that indicates that unsafe content reached a CSS or URL context.
+{{% /note %}}