I believe that the problem is with the default styling of Notepad++ for CSS files.
Go to the menu entry of Settings / Style Configurator, then click on CSS and TAG, getting this :
You will notice that the font used is @Batang (which I personally never heard of or used). This font does not look like it is a monospace font.
Change the font to the default and click Save & Close :
Here is the display, where the first image is before and the second after this change :
The second image, from after the change, looks now much more like a monospace font.
You could change the fonts some more, to better agree with Dreamweaver. However, as I do not use it, I do not know what fonts it uses for displaying CSS.