This path isn't right:url(src/assets/my-logo.jpg)
If you have put my-logo.jpg in your theme's assets folder then it will be copied into build/adapt/css/assets
when you run grunt build
or grunt dev
.
As you need to make paths relative to the CSS file, the correct path will be assets/my-logo.jpg
.
And navigation.less is probably the best place to add your .page-logo
class