Test unreachable code, fix style

Author: krassowski

atest/05_Features/Diagnostics.robot

@@ -10,4 +10,6 @@ Resource          ../Keywords.robot
 *** Test Cases ***
 Diagnostics with deprecated tag have strike-through decoration
     Wait Until Page Contains Element    css:.cm-lsp-diagnostic[title*="is deprecated"]    timeout=25s
+    Wait Until Page Contains Element    css:.cm-lsp-diagnostic[title*="Unreachable code"]    timeout=5s
     Page Should Contain Element    css:.cm-lsp-diagnostic-tag-Deprecated
+    Page Should Contain Element    css:.cm-lsp-diagnostic-tag-Unnecessary

atest/examples/Diagnostic.ipynb

@@ -59,7 +59,10 @@
     "/**\n",
     " * @deprecated\n",
     " */\n",
-    "function oldFunc() {}\n",
+    "function oldFunc(test) { \n",
+    "    return;\n",
+    "    let x = 1;\n",
+    "}\n",
     "oldFunc"
    ]
   }

packages/jupyterlab-lsp/style/highlight.css

@@ -9,11 +9,12 @@
   text-decoration-skip-ink: none;
 }
 
-.cm-lsp-diagnostic-tag-Unused {
+.cm-lsp-diagnostic-tag-Unnecessary {
   /*
    * LSP: "Clients are allowed to render diagnostics with this tag faded out instead of having an error squiggle."
    */
-  opacity: 0.85;
+  filter: grayscale(1);
+  opacity: 0.7;
   text-decoration: none !important;
 }