Refactor markup and styling

Simplified markup and culled some leftovers
Reduced CSS size
Improved source readability
Added padding to a bunch of stuff
Media query converts table to columns when <= 700px wide
Probably more? This was supposed to be several commits, but I botched it
Convert back to common CSS code style
Convert tabs back to spaces, clobbering the diffs again. Sorry. :<
Add <html>, <head>, and <body> back in
Don't link-color the countdown timer
Stretch body to viewport height when smaller
Attempt to make flexbox work nicely on Safari browsers
Restore `target="_top"` behavior via `<base>` tag
Fixed HTML tab size, for real this time
Centered credit footer, narrow-screen break, more indentation repairs
Increase site logo size to 0.9em
Merge branch 'mobile-enhancement' into gh-pages