Exercise 3, 4, and 5 completed exercises replaced with correct code

[smckinney1]

Exercise 3, exercise 4, and exercise 5 completed code should now be in sync with the end of the "HTML" segment of the Frontend Masters Web Accessibility (v3) course.

There is an issue with the completed exercises in that they contain all of the code for future exercises as well.

Issue reference

update 7/3/24: I did notice that the unchanged files in each "completed" directory should be in sync with the last completed set of code for that file, but they are not.

I'm having issues with git locally that I don't have time to troubleshoot at the moment and have had to update each file individually on my fork via GitHub.

As such I'm not going to go through all of the other files to keep them up to date.

Right now this PR is solely focused on the files changed in the video for that exercise.