RonRonnement CSS: Fix small discontinuity in the left sidebar

Commit 88aa3c3 included a small
computation mistake: the border should be taken into account in the
calculations.

Also, while it looks correct in Chrome, for some reason Firefox does not
properly position the linear gradient origin when the background is set
to repeat. We add `no-repeat` to the background specification to fix
this.

app/assets/stylesheets/parts/a_tag.scss

@@ -22,11 +22,12 @@ body {
   margin: 0 auto;
   border: solid #999;
   border-width: 0 1px;
-  background: linear-gradient(
+  background: no-repeat
+    linear-gradient(
       90deg,
       $C_CLAIR,
-      $C_CLAIR $PX_BRANDING_LARG,
-      $C_CONTAINER $PX_BRANDING_LARG,
+      $C_CLAIR $PX_BRANDING_LARG + 1px,
+      $C_CONTAINER $PX_BRANDING_LARG + 1px,
       $C_CONTAINER
     )
     #fff;

app/assets/stylesheets/parts/sidebar.scss

@@ -4,7 +4,6 @@
   text-align: left;
   font-size: 0.8em;
   line-height: 1.3;
-  background: $C_CLAIR;
 
   a {
     font-weight: inherit;