Visualforce has been in Salesforce for some years and prior to the Lightning Component framework, all custom user interfaces were built using Visualforce. Currently, there are a lot of applications on the Salesforce platform built using Visualforce, and a lot of users still use these applications with a Visualforce page. Lightning Out allows developers to use Lightning Components, developed for Lightning Experience work, in Visualforce pages.  

Salesforce also makes it easy to style Visualforce pages for a new SLDS look. An attribute named LightningStylesheets can be set to true to style Visualforce pages to look better. The code snippet for changing the stylesheet of a classic Salesforce VF is as follows:

<apex:page LightningStylesheets="true">

In this section, we will discover how to use the YouTube search component we built in Chapter 3, Lightning Component Building Blocks, to render inside a Visualforce page leveraging Lightning Out.