docs/guide/usage-widgets.md revised for readability [ci skip]

docs/guide/usage-widgets.md

@@ -19,15 +19,14 @@ framework features. All widgets belong to `\yii\bootstrap` namespace:
 - [[yii\bootstrap\Tabs|Tabs]]
 
 
-## Customize widget CSS classes <span id="widgets-customize-css-classes"></span>
+## Customizing widget CSS classes <span id="customizing-css-classes"></span>
 
-Widgets allow quick composition of the HTML for particular Bootstrap components, which requires usage of the
-Bootstrap CSS classes. Those classes are added automatically by the widgets. However usually widget provides
-fields or properties, which allow customization of the CSS styles for particular HTML tags.
+These widgets allow quick composition of the HTML for the Bootstrap components that require the use of the Bootstrap CSS classes.
+The default class for the component is added automatically by the widget, and the optional classes that you may want to customize are usually supported through the properties of the widget.
 
-For example: you may use [[yii\bootstrap\Button::options]] to customize appearance of the rendered button.
-Class 'btn' will be added automatically, so you don't need to worry about it. All you need is specify particular
-button class:
+For example, you may use [[yii\bootstrap\Button::options]] to customize the appearance of a button.
+The class 'btn' which is required for a button will be added automatically, so you don't need to worry about it.
+All you need is specify a particular button class:
 
 ```php
 echo Button::widget([
@@ -36,17 +35,16 @@ echo Button::widget([
 ]);
 ```
 
-However, sometimes you may need to replace standard class, added by the widget, with alternative one.
-For example: widget [[yii\bootstrap\ButtonGroup]] uses 'btn-group' class for the container div, but you may
-need to use 'btn-group-vertical', which allows vertical-style layout for the buttons. Using plain 'class' option
-simply adds 'btn-group-vertical' to 'btn-group', which produces incorrect result.
-In order to actually replace class added by widget, you need to specify 'class' option as array, containing
-needed class name under the 'widget' key:
+However, sometimes you may need to replace the default class with an alternative one.
+For example, the widget [[yii\bootstrap\ButtonGroup]] uses 'btn-group' class for the container div by default,
+but you may need to use 'btn-group-vertical' instead to align the buttons vertically.
+Using a plain 'class' option simply adds 'btn-group-vertical' to 'btn-group', which will produce an incorrect result.
+In order to override the default class of a widget, you need to specify the 'class' option as an array that contains the customized class name under the 'widget' key:
 
 ```php
 echo ButtonGroup::widget([
     'options' => [
-        'class' => ['widget' => 'btn-group-vertical'] // replace 'btn-group' with 'btn-group-vertical'
+        'class' => ['widget' => 'btn-group-vertical'] // replaces 'btn-group' with 'btn-group-vertical'
     ],
     'buttons' => [
         ['label' => 'A'],