Merge branch gh-pages of carpentries/styles

Author: maxim-belkin

Gemfile

@@ -5,6 +5,6 @@ source 'https://rubygems.org'
 git_source(:github) {|repo_name| "https://github.com/#{repo_name}" }
 
 # Synchronize with https://pages.github.com/versions
-ruby '>=2.5.3'
+ruby '>=2.5.8'
 
 gem 'github-pages', group: :jekyll_plugins

assets/css/lesson.scss

@@ -84,6 +84,18 @@ $color-testimonial: #fc8dc1 !default;
   border-radius: 0 0 4px 4px; // 4px == @border-radius-base
 }
 
+// Stripe above tab panels where OS tabs are shown
+ul.nav.nav-tabs {
+  background: #E1E1E1;
+  border-radius: 4px 4px 0 0;  // 4px == @border-radius-base
+}
+
+// This color provides better contrast ratio on most backgrounds used on Carpentries websites
+// 9.24 on FFFFFF: https://webaim.org/resources/contrastchecker/?fcolor=204A6F&bcolor=FFFFFF&api (body)
+// 8.78 on F9F9F9: https://webaim.org/resources/contrastchecker/?fcolor=204A6F&bcolor=F9F9F9&api (tables)
+// 7.07 on E1E1E1: https://webaim.org/resources/contrastchecker/?fcolor=204A6F&bcolor=E1E1E1&api (tab panels)
+a { color: #204A6F; }
+
 //----------------------------------------
 // Specialized blockquote environments for learning objectives, callouts, etc.
 //----------------------------------------