There is no need to fix this unless you REALLY feel the gap is taking away from your entire kitchen experience. If you wish to add more expense, you are welcome to contact the cabinet makers and ask them if they can make a small piece of finishing to mount above the dishwasher to hide this gap. It won't be cheap...but it will work.

The other option is: remove dishwasher, add 1/2" plywood "platform" to the floor (nailed/glued in place naturally) and then reinstall dishwasher. This will cost the price of 1/2" plywood ($18- $32 sheet), some nails/screws/glue, a plumber to make a house call for the 3 hour minimum they charge (in Canada that is $80/hr + labour).

Many dishwashers have 1/2" - 3/4" gap or clearance to the counter top. This is not unusual. Many manufacturers require a certain amount of "clearance" to the top of the counter top/sides of the cabinets due to heat and humidity that comes of the machine. That's why I suggested a 1/2" plywood and nothing thicker. You need a certain amount of clearance.