Add the "Sass: Parent selector" page.

Author: paveloom

content/notes/Sass_Parent_selector.md

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++++
+title = "Sass: Parent selector"
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+
+In Sass files, when a parent selector (`&`) is used in an inner selector, it's replaced with the corresponding outer selector.
+
+For example,
+
+```scss
+.alert {
+  // The parent selector can be used to add pseudo-classes to the outer
+  // selector.
+  &:hover {
+    font-weight: bold;
+  }
+
+  // It can also be used to style the outer selector in a certain context, such
+  // as a body set to use a right-to-left language.
+  [dir=rtl] & {
+    margin-left: 0;
+    margin-right: 10px;
+  }
+
+  // You can even use it as an argument to pseudo-class selectors.
+  :not(&) {
+    opacity: 0.8;
+  }
+}
+```