You automatically get a vertical scroll bar on every page and blog post that you create in WordPress. But you can’t automatically add a horizontal scroll bar to WordPress as it comes out of the box.
Here are some resources on adding a horizontal scroll bar without a plugin (just using the HTML and CSS):
How To View the HTML Source in Google Chrome: Learn how a website was built by viewing its source code by Updated August 14, 2019.
How to Build a Horizontal Scrolling WordPress Blog
by Brandy Alexander from Small Business Chron. Accessed 10-18-2019:
Your WordPress blog produces a vertical scrollbar when you have a long page of content, but you do not automatically get a horizontal scroll feature if you have a wide page. Horizontal scrolling is ideal if you have elements, such as photos, that widen your site because this bar appears at the bottom of the browser window and lets the visitor scroll from left to right. Use the tools in your WordPress account to apply the Cascading Style Sheets code that produces horizontal scrolling on your blog.
WordPress relies heavily on the presentation styles within CSS. With the use of Themes, you have an almost infinite choice of layout options. WordPress Themes make it easy to change your website’s appearance, and open up the field to help you create your own Theme and page layout.
CSS stands for Cascading Style Sheets. It allows you to store style presentation information (like colors and layout) separate from your HTML structure. This allows precision control of your website layout and makes your pages faster and easier to update.
This article briefly describes the use of CSS in WordPress, and lists some references for further information. For information on CSS itself, see Know Your Sources#CSS.