A sidebar is known so because it either stays at the left or right side of the browser. The sidebar is basically vertical column provided by the theme to display every other information except content.
Sidebars usually include a Search bar, Archives, Categories, Links, Contact forms, A few gallery pictures, Twitter / Instagram (other social media) feeds. But it’s not limited to just these. You can include text boxes for your introduction as an author or business and much more using Avoori widgets!
The slider lets you choose the sidebar width. First, you need to take into account the content width. So if you have chosen 70% to be your content width. You can use the remaining up to 30% for the sidebar.
Sidebars aren’t usually more than 30% but mostly amongst 20% to 30%.