From where I can install Accessibility toolkit in magento?

The Accessibility Toolkit adds a one-click accessibility widget to your Magento storefront — text-to-speech, contrast and grayscale modes, font resizing, link and heading highlighting, reading focus and keyboard navigation — giving shoppers control over how your pages look and read, without editing your theme code. It is an assistive preference toolbar, not a compliance product: WCAG and ADA conformance still depends on your own theme's markup.

You can install Accessibility from here.

After installing

Go to Stores → Configuration → AppifyCommerce → Accessibility Toolkit in your Magento admin.
Make sure Status is Enable, then pick an icon position and style that match your theme.
Under Advance Settings, optionally add your accessibility-statement link, choose the widget's default language and add custom CSS.
Click Save Config and flush the cache. The widget is enabled by default and appears on every storefront page.

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After installing​

After installing