docs: add api doc for ng_style directive (#27379)

PR Close #27379

packages/common/src/directives/ng_style.ts

@@ -12,21 +12,34 @@ import {Directive, DoCheck, ElementRef, Input, KeyValueChanges, KeyValueDiffer,
  * @ngModule CommonModule
  *
  * @usageNotes
+ *
+ * Set the font of the containing element to the result of an expression.
+ *
  * ```
  * <some-element [ngStyle]="{'font-style': styleExp}">...</some-element>
+ * ```
  *
+ * Set the width of the containing element to a pixel value returned by an expression.
+ *
+ * ```
  * <some-element [ngStyle]="{'max-width.px': widthExp}">...</some-element>
+ * ```
  *
+ * Set a collection of style values using an expression that returns key-value pairs.
+ *
+ * ```
  * <some-element [ngStyle]="objExp">...</some-element>
  * ```
  *
  * @description
  *
- * Update an HTML element styles.
+ * An attribute directive that updates styles for the containing HTML element.
- *
+ * Sets one or more style properties, specified as key-value pairs.
- * The styles are updated according to the value of the expression evaluation:
+ * The key is a style name, with an optional `.<unit>` suffix (such as 'top.px', 'font-style.em').
- * - keys are style names with an optional `.<unit>` suffix (ie 'top.px', 'font-style.em'),
+ * The value is an expression to be evaluated.
- * - values are the values assigned to those properties (expressed in the given unit).
+ * The resulting non-null value, expressed in the given unit,
+ * is assigned to the given style property.
+ * If the result of evaluation is null, the corresponding style is removed.
  *
  * @publicApi
  */