turn on styleSelectedText by default, add style for selected search text

packages/codemirror/src/editor.ts

@@ -1244,7 +1244,7 @@ export namespace CodeMirrorEditor {
     lineWiseCopyCut: true,
     scrollPastEnd: false,
     styleActiveLine: false,
-    styleSelectedText: false,
+    styleSelectedText: true,
     selectionPointer: false,
     rulers: [],
     foldGutter: false

packages/codemirror/style/index.css

@@ -107,6 +107,10 @@ pre.CodeMirror-line {
   margin-right: -5px;
 }
 
+.CodeMirror-selectedtext.cm-searching {
+  background-color: orangered !important;
+}
+
 .CodeMirror-focused .CodeMirror-selected {
   background-color: var(--jp-editor-selected-focused-background);
 }