Designing 'Pixel Perfect' is exactly as it sounds. When handing over designs to developers I find it key to understand which programmes the developers prefer to use, this way the assets are totally translatable to their developments.
In this case (and many) the developers at Like Digital (agency) prefer for the assets to be designed in Sketch - a vector based programme causing a real stir in the design industry with its minimal interface and accessible price point in comparison to the likes of Adobe (that's a discussion for another time!)
Here you can see the mid-fidelity responsive Hardy Amies, Savile Row tailors website which has been designed pixel perfect for both desktop and mobile in Sketch. Have a scroll!