Styling changes:

- move `usa-accordion` class to wrap all accordion elements
- remove background color form `accordion` class and move it to atat
specific class `accordion__header`
- create class names for styling elements instead of relying on element
type

styles/elements/_accordions.scss

@@ -2,13 +2,12 @@
   @include shadow-panel;
   margin: $gap * 3 0;
   max-width: $max-panel-width;
-  background-color: $color-white;
 
   &__header {
     padding: $gap * 2 $gap * 3;
+    background-color: $color-white;
 
-    h3,
-    p {
+    &-text {
       margin: 0;
     }
   }