I have done the 4th project now and would like to receive any feedback. Positive and negative welcome. What to improve, what is wrong, what should I stick to etc.
You should remove the float on the #navbar when you stack the page, otherwise, you have to give it a z-index to make the links clickable. Just set the float to none in the media query you have.
Not sure if it is intended that the nav is not the full height of the page (if not just add height: 100%; to it) but I actually kind of like the look it gives. I’m just not sure it’s height should be so arbitrary may be set a height less than 100% so you have a rule for how tall it should be. That will also let you remove the invalid <br> elements (The <br> element cannot be a child of the <ul> element.)