renp

A simple WordPress plugin which adds a “scroll to top” button to the bottom corner of the page if the page has been scrolled down. It is compatible with all major browsers and should work with all themes, including 
responsive and high resolution themes.
It is possible to configure the plugin in the admin area for choosing between light or dark colour schemes and size of the button as well.
If your theme doesn’t already contain this feature, you can simply add it by means of this plugin.

Scroll to Top Button

Displays a button in the bottom right corner for smooth scrolling to the top of the page.

Felix Arntz

This plugin takes a no-frills approach to smooth scrolling, providing a fast, performant, and accessible user experience.
Simply enable the plugin, and any anchor links (i.e. links that point to other content on the same page) will provide a smooth scrolling experience rather than abruptly jumping to the destination content.
The plugin relies on the latest smooth scrolling techniques using CSS. A very fast and lightweight JavaScript polyfill (<1KB) is included to equally support older browsers, including Internet Explorer. So you can rest assured this plugin covers your userbase.
<h4>Why does this plugin exist?</h4>

Smooth scrolling is a basic feature to enhance user experience, so it shouldn’t come at a performance cost that at the same time harms user experience elsewhere.
Several other smooth scrolling solutions unfortunately rely on outdated techniques such as jQuery, which can hurt your site’s performance, and is really not necessary to provide the feature. Even browsers as old as 10 years don’t need jQuery to achieve smooth scrolling. In fact, as of today you can achieve the behavior with only CSS, not even requiring any JavaScript.
Another potential reason to use this plugin over other smooth scrolling solutions is accessibility: This plugin respects the user preferences around reduced motion, which can avoid discomfort for those with <a href="https://www.a11yproject.com/posts/understanding-vestibular-disorders/" rel="nofollow ugc">vestibular motion disorders</a>.
You may already use a smooth scrolling plugin, but it is worth double checking that it doesn’t use one of those outdated, inefficient, and inaccessible approaches that may slow down your site or affect user interactions negatively.
<h4>More technical details</h4>
This plugin simply enables smooth scrolling with the <code>scroll-behavior</code> CSS property. This property has been supported by all modern browsers for a few years now.
To support older browsers as well, a lightweight JavaScript polyfill is included, which is only loaded for browsers that lack support for the CSS property and doesn’t require any dependencies. The polyfill uses latest JavaScript user experience best practices such as <code>requestAnimationFrame</code> to provide a smooth scrolling experience without potentially blocking other user interactions.
For relevant browser support, see: 
* <a href="https://caniuse.com/css-scroll-behavior" rel="nofollow ugc">CSS Scroll-behavior</a> 
* <a href="https://caniuse.com/mdn-css_properties_scroll-padding-top" rel="nofollow ugc">CSS property: scroll-padding-top</a> 
* <a href="https://caniuse.com/prefers-reduced-motion" rel="nofollow ugc">prefers-reduced-motion media query</a> 
* <a href="https://caniuse.com/requestanimationframe" rel="nofollow ugc">requestAnimationFrame</a> 
* <a href="https://caniuse.com/high-resolution-time" rel="nofollow ugc">High Resolution Time API</a> 
* <a href="https://caniuse.com/mdn-api_nodelist" rel="nofollow ugc">NodeList API</a> 
* <a href="https://caniuse.com/mdn-api_window_scrollto" rel="nofollow ugc">Window API: scrollTo</a>

Fast Smooth Scroll

This lightweight plugin enhances user experience by enabling smooth scrolling for anchor links without the need for jQuery or other dependencies.

Scroll to Top Button vs Fast Smooth Scroll