OS Details

Google Pixel 2 XL has been launched in October 2017.
Google Pixel 2 XL have Android 8.0 (Oreo)

Screen Dimensions

Google Pixel 2 XL screen size is 6.0 inch with ~ 76.4% body ratio of actual device size. Physical dimensions for Google Pixel 2 XL device is 6.22 x 3.02 x 0.31 INCH or ( 157.9 x 76.7 x 7.9 MM).

Displaying of Units are in this order "Height x Width x Thickness"

Screen Pixel Density and CSS Pixel Ratio

"Pixel" is smallest unit/element of any display.

The total number of pixels that fit into an inch is referred to as "Screen Density" or "Pixel Density" and it measured as "Pixels Per Inch".
Pixel Desnsity have limits to display Pixels Per Inch depends on different screen sizes. When number of pixels per inch increases than it's screen-size limit, the Display resolution will increase but actual device width/height in pixels remain same. Actual device pixels are known as Device Independent Pixels or CSS Pixel Ratio.

Google Pixel 2 XL resolution is 1440 x 2880 ^PX with ~ 538 pixel desnsity.
Google Pixel 2 XL viewport size is 412 x 823 ^PX with ~ 154 actual pixel density, which means it have 3.5 xxxhdpi display pixel density.

Screen Resolution and Viewport

The sum of pixels which are displaying on a device is called as "Screen Resolution". and sum of actual pixels of any device is reffered to as "Viewport".

Google Pixel 2 XL have 6.0" physical screen size and its resolution is about 1440 x 2880 Pixels with approximately 538 PPI pixel density. Google Pixel 2 XL has viewport size 412 x 823 Pixels and its pixel ratio is about 3.5.

For better understanding screen actual sizes, viewport sizes, display resolution and about their density click here.

CSS Media Queries

Google Pixel 2 XL Media Queries (In terms of Mobile only)

@media only screen and (min-width: 412px) and (max-width: 767px) { /* Your Styles... */ }

Google Pixel 2 XL Min-Width Media Queries

@media only screen and (min-width: 412px) { /* Your Styles... */ }

Google Pixel 2 XL Min-Height Media Queries

@media only screen and (min-height: 823px) { /* Your Styles... */ }

Google Pixel 2 XL Landscape Media Queries

@media only screen and (min-width: 823px) and (orientation: landscape) { /* Your Styles... */ }

Google Pixel 2 XL Portrait Media Queries

@media only screen and (min-width: 412px) and (orientation: portrait) { /* Your Styles... */ }

Google Pixel 2 XL Device Width Media Queries

@media only screen and (min-device-width: 412px) and (orientation: portrait) { /* Your Styles... */ }
@media only screen and (min-device-width: 823px) and (orientation: landscape) { /* Your Styles... */ }

Google Pixel 2 XL Retina Media Queries

@media
  only screen and (-webkit-min-device-pixel-ratio: 3.5),
  only screen and (   min--moz-device-pixel-ratio: 3.5),
  only screen and (     -o-min-device-pixel-ratio: 3.5/1),
  only screen and (        min-device-pixel-ratio: 3.5),
  only screen and (                min-resolution: 538dpi),
  only screen and (                min-resolution: 3.5dppx) { 
    /* Retina styles here */
}
                                

Retina is actually based upon device pixel ratio. Devices mostly have 2x or 3x display so you can use general retina media queries to display high resolution content on all kind of devices. Retina 2x and Retina 3x media queries given below:

Retina 2x Media Query

@media
  only screen and (-webkit-min-device-pixel-ratio: 2),
  only screen and (   min--moz-device-pixel-ratio: 2),
  only screen and (     -o-min-device-pixel-ratio: 2/1),
  only screen and (        min-device-pixel-ratio: 2),
  only screen and (                min-resolution: 192dpi),
  only screen and (                min-resolution: 2dppx) { 
    /* Retina styles here */
}
                                

Retina 3x Media Query

@media
  only screen and (-webkit-min-device-pixel-ratio: 3),
  only screen and (   min--moz-device-pixel-ratio: 3),
  only screen and (     -o-min-device-pixel-ratio: 3/1),
  only screen and (        min-device-pixel-ratio: 3),
  only screen and (                min-resolution: 384dpi),
  only screen and (                min-resolution: 3dppx) { 
    /* Retina styles here */
}
                                

Google Pixel 2 XL Specifications

• Launch Date October 2017
• Android 8.0
• Physical Screen Size 6.0 INCH
• Resolution 1440 x 2880 PX
• Viewport Size 412 x 823 PX
• Pixel Density 538 PPI
• Device-Independent Pixels 154 PPI
• Pixel Ratio 3.5 xxxhdpi
• Width 1440 PX
• Height 2880 PX
• Device Width 412 PX
• Device Height 823 PX
• Dimensions 157.9 x 76.7 x 7.9 mm (6.22 x 3.02 x 0.31 in)
• Weight 175 g - 6.17 oz