iPhone X

@media only screen 
    and (device-width : 375px) 
    and (device-height : 812px) 
    and (-webkit-device-pixel-ratio : 3) { }

iPhone 8

@media only screen 
    and (device-width : 375px) 
    and (device-height : 667px) 
    and (-webkit-device-pixel-ratio : 2) { }

iPhone 8 Plus

@media only screen 
    and (device-width : 414px) 
    and (device-height : 736px) 
    and (-webkit-device-pixel-ratio : 3) { }

iPhone 6+/6s+/7+/8+ share the same sizes, while the iPhone 7/8 also do.

Looking for a specific orientation ?

Portrait

Add the following rule:

    and (orientation : portrait) 

Landscape

Add the following rule:

    and (orientation : landscape) 

References:

• https://webkit.org/blog/7929/designing-websites-for-iphone-x/
• https://developer.apple.com/ios/human-interface-guidelines/visual-design/adaptivity-and-layout/
• https://developer.apple.com/ios/human-interface-guidelines/overview/iphone-x/
• https://mydevice.io/devices/
• http://viewportsizes.com/mine/

I noticed that the answers here are using: device-width, device-height, min-device-width, min-device-height, max-device-width, max-device-height.

Please refrain from using them since they are deprecated. see MDN for reference. Instead use the regular min-width, max-width and so on. For extra assurance, you can set the min and max to the same px amount. For example:

iPhone X

@media only screen 
    and (width : 375px) 
    and (height : 812px)
    and (orientation : portrait)  
    and (-webkit-device-pixel-ratio : 3) { }

Here are a few useful links on this subject:

• https://medium.com/@hacknicity/how-ios-apps-adapt-to-the-iphone-x-screen-size-a00bd109bbb9
• https://developer.apple.com/design/human-interface-guidelines/ios/visual-design/adaptivity-and-layout/
• https://ivomynttinen.com/blog/ios-design-guidelines
• https://www.paintcodeapp.com/news/ultimate-guide-to-iphone-resolutions

It seems that the most accurate (and seamless) method of adding the padding for iPhone X/8 using env()...

padding: env(safe-area-inset-top) env(safe-area-inset-right) env(safe-area-inset-bottom) env(safe-area-inset-left);

Here's a link describing this:

https://css-tricks.com/the-notch-and-css/

If your page is missing meta[@name="viewport"] element within its DOM, then the following could be used to detect a mobile device:

@media only screen and (width: 980px), (hover: none) { … }

If you want to avoid false-positives with desktops that just magically have their viewport set to 980px like all the mobile browsers do, then a device-width test could also be added into the mix:

@media only screen and (max-device-width: 800px) and (width: 980px), (hover: none) { … }

Per the list at https://developer.mozilla.org/en-US/docs/Web/CSS/Media_Queries/Using_media_queries, the new hover property would appear to be the final new way to detect that you've got yourself a mobile device that doesn't really do proper hover; it's only been introduced in 2018 with Firefox 64 (2018), although it's been supported since 2016 with Android Chrome 50 (2016), or even since 2014 with Chrome 38 (2014):

• https://developer.mozilla.org/en-US/docs/Web/CSS/@media/hover