Delete unnecessary css format for .subcontainer

delete css format for not existing elements

change the text color for .lorem

change border-width of nav to polish the display

change the css format of nav div to display nav element not in a line, more readablein small screen

change the media queries screen scale division from 12.5em to 18.5em, making the nav div display clearly in both neighboring screen scales

Adding css format for nav div to make the nav at bottom displayed differently from the smaller screen due to the different scale