Editor type scales for real: drop prosekit typography.css, fix selectors

The earlier rem override never matched: editor.mount() turns the
.prosekit-editor div itself into the .ProseMirror root, so
'.prosekit-editor .ProseMirror p' selected nothing and prosekit
typography.css's fixed 16px kept winning. Verified by mounting the
editor standalone and reading the mount div's classes.

Rather than out-specificity a stylesheet we don't control, stop
loading it: prosekit's typography.css is optional px-based sugar. Our
own rem scale (now selected as direct children of .prosekit-editor)
plus UA em defaults for lists/blockquote/code is the whole editor
typography, all tracking the responsive root.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

prosekit-editor.js

@@ -285,8 +285,11 @@ function buildToolbar(editor) {
 }
 
 export function mountEditor(container, hiddenInput, initial) {
+  // Only the structural stylesheet (placeholder, lists, gap cursor).
+  // Deliberately NOT prosekit/basic/typography.css: it sizes content in
+  // fixed px, which fights the app's responsive root font-size. All
+  // editor typography lives in our own stylesheet, in rem.
   ensureStylesheet('https://esm.sh/prosekit/basic/style.css')
-  ensureStylesheet('https://esm.sh/prosekit/basic/typography.css')
 
   const extension = union(
     defineBasicExtension(),

style/main.css

@@ -450,6 +450,7 @@ textarea:focus {
    placeholder pseudo-element, which read far dimmer than the
    native inputs next to it. */
 ::placeholder,
+.prosekit-editor .prosekit-placeholder::before,
 .prosekit-editor.prosekit-placeholder::before {
   color: var(--ink-dim);
   opacity: 1;
@@ -508,57 +509,60 @@ textarea:focus {
   box-shadow: 0 0 0 0.18rem var(--accent-soft);
 }
 
-/* ProseKit's typography.css (loaded from esm.sh at mount time) sets
-   fixed px font sizes on .ProseMirror, so they ignore the responsive
-   root font-size. Re-state them in rem/em at the same proportions,
-   with .prosekit-editor prefixed so these win on specificity. */
-.prosekit-editor .ProseMirror p {
+/* The editor's whole type scale, in rem. ProseKit's own typography.css
+   is deliberately not loaded (it sizes content in fixed px - see
+   mountEditor in prosekit-editor.js), so these rules are the only
+   typography the editor gets, on top of UA defaults (em-based, they
+   scale fine for lists/blockquote/code). NOTE: editor.mount() turns the
+   .prosekit-editor div itself into the .ProseMirror root, so content
+   elements are its direct children - no .ProseMirror in the selector. */
+.prosekit-editor p {
   font-size: 1rem;
   line-height: 1.5;
   margin: 0 0 0.6em;
 }
 
-.prosekit-editor .ProseMirror p:last-child {
+.prosekit-editor p:last-child {
   margin-bottom: 0;
 }
 
-.prosekit-editor .ProseMirror h1 {
+.prosekit-editor h1 {
   font-size: 2.5rem;
   line-height: 1.1;
   margin: 0.9em 0 0.1em;
 }
 
-.prosekit-editor .ProseMirror h2 {
+.prosekit-editor h2 {
   font-size: 1.875rem;
   line-height: 1.3;
   margin: 1.05em 0 0.13em;
 }
 
-.prosekit-editor .ProseMirror h3 {
+.prosekit-editor h3 {
   font-size: 1.5rem;
   line-height: 1.33;
   margin: 0.9em 0 0.04em;
 }
 
-.prosekit-editor .ProseMirror h4 {
+.prosekit-editor h4 {
   font-size: 1.25rem;
   line-height: 1.3;
   margin: 0.8em 0 0.05em;
 }
 
-.prosekit-editor .ProseMirror h5 {
+.prosekit-editor h5 {
   font-size: 1.125rem;
   line-height: 1.22;
   margin: 0.78em 0 0.06em;
 }
 
-.prosekit-editor .ProseMirror h6 {
+.prosekit-editor h6 {
   font-size: 1rem;
   line-height: 1.25;
   margin: 0.75em 0 0.06em;
 }
 
-.prosekit-editor .ProseMirror :is(h1, h2, h3, h4, h5, h6):first-child {
+.prosekit-editor :is(h1, h2, h3, h4, h5, h6):first-child {
   margin-top: 0;
 }