Constrain max width to 960px on docs content pages (#1593)

Fixes #1458

Author: fertolg

src/_assets/css/_content.scss

@@ -17,6 +17,10 @@
   padding-bottom: $site-content-top-padding;
   padding-top: $site-content-top-padding;
 
+  .container {
+    max-width: $site-content-max-width;
+  }
+
   @include media-breakpoint-up(md) {
     border-left: 1px solid $site-color-light-grey;
     min-height: calc(100vh - #{$site-header-height} - #{$site-footer-md-default-height});

src/_assets/css/_variables.scss

@@ -22,6 +22,7 @@ $site-font-icon: 24px/1 $site-font-family-icon;
 $site-header-height: 66px;
 $site-footer-md-default-height: 140px;
 $site-content-top-padding: 40px;
+$site-content-max-width: 960px;
 $site-nav-mobile-side-padding: 20px;
 
 // Layer stack