Using Chrome:
1) Open Developer Tools window (ctrl-shift-I)
2) Toggle Device Menu (ctrl-shift-M or 2nd icon in top menu bar)
The browser window changes to show the Device Menu and resize the document "viewport" to fit various device sizes
* Use "Responsive" dropdown list to select from some common devices... choose "edit..." to add other pre-defined devices or define your own custom device
* Use input fields provided in the device menu to hand-enter custom device dimensions
* Use "Percentage" dropdown to select current device "zoom" level or toggle "Auto-adjust zoom"
* Use "Throttling" menu to adjust display performance (no throttling, mid-tier mobile, low-end mobile, or offline)
* Click "rotate" icon to switch display mode between portrait (vertical) and landscape (horizontal)
* Click on hot zones in bar below Device Menu to quickly switch device pixel width (from "Mobile Small 320px" through "4K 2560px")
* On far right of Device Menu is "three dots" menu dropdown with more options, including:
* Show/Hide Device Frame, Media Queries, Rulers
* Add/Remove Device Pixel Ratio and Device Type controls
* Capture Screenshot, Full-Size Screenshot
* Reset to Defaults (resets device menu to default settings)
* Close DevTools (removes device menu and resets to normal browser window display)
enjoy,
-e