docs: Update docs for m.io site update.

PiperOrigin-RevId: 345491088

Author: joyzhong

packages/mdc-banner/README.md

@@ -13,7 +13,7 @@ A banner displays a prominent message and related optional actions.
 
 ![Banner example](images/banner.png)
 
-## Content
+**Contents**
 
 * [Using banners](#using-banners)
 * [Banners](#banners)

packages/mdc-checkbox/README.md

@@ -19,7 +19,7 @@ Use checkboxes to:
 
 ![Checkbox hero example for menu options](images/checkbox-hero.png)
 
-## Contents
+**Contents**
 
 * [Using checkboxes](#using-checkboxes)
 * [Checkboxes](#checkboxes)

packages/mdc-drawer/README.md

@@ -13,7 +13,7 @@ path: /catalog/drawers/
 
 ![Hero navigation drawer image](images/drawer-hero.png)
 
-## Contents
+**Contents**
 
 * [Using navigation drawers](#using-navigation-drawers)
 * [Types](#types)

packages/mdc-progress-indicator/README.md

@@ -8,6 +8,7 @@ path: /catalog/progress-indicator/
 -->
 
 # Progress Indicators
+
 The MDC Progress Indicator component exposes common foundation and component interfaces for a progress indicator. Components that implement these interfaces include [linear progress](https://github.com/material-components/material-components-web/tree/master/packages/mdc-linear-progress) and [circular progress](https://github.com/material-components/material-components-web/tree/master/packages/mdc-circular-progress).
 [Material Design progress & activity requirements](https://material.io/go/design-progress-indicators).
 

packages/mdc-radio/README.md

@@ -18,7 +18,7 @@ Use radio buttons to:
 
 ![Radio button hero example for menu options](images/radio-button-hero.png)
 
-## Contents
+**Contents**
 
 * [Using radio buttons](#using-radio-buttons)
 * [Radio buttons](#radio-buttons)

packages/mdc-slider/README.md

@@ -16,7 +16,7 @@ The MDC Slider implementation supports both single point sliders (one thumb)
 and range sliders (two thumbs). It is backed by the browser
 `<input type="range">` element, is fully accessible, and is RTL-aware.
 
-## Contents
+**Contents**
 
 *   [Using sliders](#using-sliders)
 *   [Sliders](#sliders)

packages/mdc-switch/README.md

@@ -14,7 +14,7 @@ Switches toggle the state of a single setting on or off. They are the preferred
 
 ![Switch hero example for menu options](images/switch-hero.png)
 
-## Contents
+**Contents**
 
 * [Using switches](#using-switches)
 * [Switches](#switches)

packages/mdc-tooltip/README.md

@@ -13,7 +13,7 @@ Tooltips display informative text when users hover over, focus on, or tap an ele
 
 ![Tooltip example](images/tooltip.png)
 
-## Contents
+**Contents**
 
 * [Using tooltips](#using-tooltips)
 * [Tooltips](#tooltips)