Make focused styles more specific.

So that they no longer leak into nested editors.

FIX: Make sure styles targeting the editor's focus status are specific enough
to not cause them to apply to editors nested inside another focused editor. This
will require themes to adjust their selection background styles to match the new
specificity.

See https://discuss.codemirror.net/t/remove-blinking-cursor-inside-the-widget-with-cm-instance/6284

src/theme.ts

@@ -100,17 +100,17 @@ export const baseTheme = buildTheme("." + baseThemeID, {
   "&dark .cm-selectionBackground": {
     background: "#222"
   },
-  "&light.cm-focused .cm-selectionBackground": {
+  "&light.cm-focused > .cm-scroller > .cm-selectionLayer .cm-selectionBackground": {
     background: "#d7d4f0"
   },
-  "&dark.cm-focused .cm-selectionBackground": {
+  "&dark.cm-focused > .cm-scroller > .cm-selectionLayer .cm-selectionBackground": {
     background: "#233"
   },
 
   ".cm-cursorLayer": {
     pointerEvents: "none"
   },
-  "&.cm-focused .cm-cursorLayer": {
+  "&.cm-focused > .cm-scroller > .cm-cursorLayer": {
     animation: "steps(1) cm-blink 1.2s infinite"
   },
 
@@ -135,7 +135,7 @@ export const baseTheme = buildTheme("." + baseThemeID, {
     position: "absolute"
   },
 
-  "&.cm-focused .cm-cursor": {
+  "&.cm-focused > .cm-scroller > .cm-cursorLayer .cm-cursor": {
     display: "block"
   },