Remove experiments with ::before and ::after

I was trying to see how far I could get with avoiding wrapping elements 
to achieve sections as full-width bands. There are some exciting CSS 
things being discussed:

* A [::wrapper pseudo 
element](w3c/csswg-drafts#588) seems stalled 
because it could cause some tricky situations in the DOM, but
* A [::contents pseudo 
element](w3c/csswg-drafts#2406) is still under 
consideration and has some steam.

_sass/home.scss

@@ -14,20 +14,6 @@ body {
 header, section {
   margin: 0 auto;
   max-width: 60rem;
-
-  &::before {
-    width: 10px;
-    height: 100px;
-    background-color: green;
-    content: ' ';
-  }
-
-  &::after {
-    width: 10px;
-    height: 100px;
-    background-color: green;
-    content: ' ';
-  }
 }
 
 .conference-home header {