Fix two small UI issues (README bg color, Script & Interactive info) (#9385)

* Fix Script & Interactive tab alert message

Fix #9354

* Fix background color section for README sections

Fix color constrast issue on the upload page
Fix #9355

Author: joelverhagen

src/Bootstrap/dist/css/bootstrap-theme.css

@@ -2,8 +2,7 @@
   .readme-container {
     display: block;
     padding: 10.5px;
-    background-color: @pre-bg;
-    border: 1px solid #ccc;
+    border: 2px solid #ccc;
     word-break: normal;
     margin-bottom: @default-margin-bottom;
     overflow: auto;
@@ -44,7 +43,7 @@
 
   pre {
     code.hljs {
-      background-color: #f6f8fa;
+      background-color: @pre-bg;
       color: #24292e; 
 
       .hljs-doctag,
@@ -92,7 +91,7 @@
       .hljs-comment,
       .hljs-code,
       .hljs-formula {
-        color: #6a737d;
+        color: #646d76;
       }
 
       .hljs-name,

src/Bootstrap/less/theme/common-readme.less

@@ -143,7 +143,7 @@
                 CommandPrefix = "> ",
                 InstallPackageCommands = new [] { string.Format("#r \"nuget: {0}, {1}\"", Model.Id, Model.Version) },
                 AlertLevel = AlertLevel.Info,
-                AlertMessage = "#r directive can be used in F# Interactive, C# scripting and .NET Interactive. Copy this into the interactive tool or source code of the script to reference the package."
+                AlertMessage = "#r directive can be used in F# Interactive and Polyglot Notebooks. Copy this into the interactive tool or source code of the script to reference the package."
             },
 
             new ThirdPartyPackageManagerViewModel("Cake", "https://cakebuild.net/support/nuget")