Did you add the door icon from the classic icons or from elsewhere?
Can you give more detail or post a picture to describe how they look different?
If the icon is from other than classic see this post for how to use the classic icon’s to show door open and closed.
You can also try using the MAP transformation in your items file to change ON/OFF to OPEN/CLOSED. This might change the look to be similar to the rest?
Example
Switch Your_Item "Your Switch Item [MAP(door.map):%s]" <door>
door.map file
ON=OPEN
OFF=CLOSE
EDIT: If using MAP transformation be sure to add this via PaperUI > Addons > Transformations and create the door.map file in /etc/openhab2/transform (linux system)