Add a snippet with the percentage syntax.

docs/styles/css_units/percentage.md

@@ -1 +1,27 @@
 # Percentage
+
+## Syntax
+
+--8<-- "docs/styles/snippets/percentage_syntax.md"
+
+!!! warning
+
+    Not to be confused with the [fractional](./fractional.md) unit nor with the [scalar](./scalar.md) unit.
+
+## Examples
+
+```css
+Widget {
+    background: red 70%;
+}
+```
+
+```py
+widget.styles.background = "red 70%"
+```
+
+## Used by
+
+ - [`background`](../background.md)
+ - [`color`](../color.md)
+ - [`tint`](../tint.md)

docs/styles/snippets/percentage_syntax.md

@@ -0,0 +1,2 @@
+A percentage is a number followed by the percent sign.
+The number doesn't have to be an integer and values are clamped between 0% and 100%.