refactor(shared): consolidate empty-state into shared chrome (BEM)

Three tools (archive, browse, classifier) independently implemented
an empty-state pattern with three different CSS class naming
conventions and slightly different rules:

  archive:    .empty-state + .empty-state-content (BEM-less)
  browse:     .empty-state + .empty-state__inner  (BEM)
  classifier: .empty-state + .empty-state-content (BEM-less)

Same visual intent ("nothing's loaded yet — here's a welcome card
with instructions"), implemented three times with subtly different
spacing, no shared body styling for h2/p/ul/li, and incompatible
class names that prevented a future tool from copy-pasting the
pattern.

Promote a single consolidated rule set to shared/base.css using
BEM naming throughout:

  .empty-state                       — base (flex centered, padding)
  .empty-state--overlay              — modifier: position absolute,
                                        top 50px to clear app-header,
                                        z-index 10. Used by archive
                                        and classifier (their empty
                                        states sit OVER the main
                                        layout).
  .empty-state__inner                — content card (left-aligned,
                                        text-muted, max-width 640)
  .empty-state__inner--centered      — modifier: tighter max-width
                                        500, centered text, 2rem
                                        padding. Used by tools whose
                                        welcome screen reads as a
                                        centered card.
  .empty-state__inner h2/p/ul/ol/li  — typography defaults
  .empty-state__inner .note          — italic small-print
  .welcome-list                      — bullet list with left-aligned
                                        text + auto margins; safe to
                                        nest inside a centered card.

Per-tool changes:

  - archive/template.html, archive/js/app.js: rename
    .empty-state-content → .empty-state__inner empty-state__inner--centered;
    add .empty-state--overlay to the outer .empty-state container.
    Also the runtime-injected unsupported-browser markup in
    showUnsupportedBrowserMessage() and the showHttpErrorState
    selector.
  - classifier/template.html: same renames.
  - archive/css/layout.css + components.css: delete .empty-state*
    and .welcome-list rules (now in shared).
  - classifier/css/layout.css: same. Keep .empty-state.drag-over
    locally — classifier is the only tool whose empty state acts
    as a drop target.
  - browse/css/base.css: delete .empty-state* (shared covers it).
    browse's template was already using .empty-state__inner so no
    template change needed.

LOC: shared/base.css gains ~70 lines; per-tool overrides lose ~85
combined. Net -15. More importantly, future tools can reuse the
pattern by adding two divs and (optionally) the --centered or
--overlay modifiers; no copy-paste required.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

archive/css/components.css

@@ -643,12 +643,7 @@ input[type="checkbox"] {
     color: var(--text-muted);
 }
 
-/* ── Welcome screen list ─────────────────────────────────────────────────── */
+/* .welcome-list lives in shared/base.css. */
-.welcome-list {
-    text-align: left;
-    margin: 0.5rem auto;
-    max-width: 400px;
-}
 
 /* ── Windows path tip (inside welcome screen) ────────────────────────────── */
 .windows-tip {

archive/css/layout.css

@@ -191,24 +191,7 @@
 }
 
 /* Empty State — positioned below the app header */
-.empty-state {
+/* .empty-state / .empty-state__inner / .welcome-list live in shared/base.css. */
-    position: absolute;
-    top: 50px; /* clear the header */
-    left: 0;
-    right: 0;
-    bottom: 0;
-    display: flex;
-    align-items: center;
-    justify-content: center;
-    background: var(--bg);
-    z-index: 10;
-}
-
-.empty-state-content {
-    text-align: center;
-    max-width: 500px;
-    padding: 2rem;
-}
 
 /* Project warning banner */
 .project-warning-banner {
@@ -233,16 +216,6 @@
     flex-shrink: 0;
 }
 
-.empty-state-content h2 {
-    color: var(--text);
-    margin-bottom: 1rem;
-}
-
-.empty-state-content p {
-    margin-bottom: 1rem;
-    color: var(--text-muted);
-}
-
 /* Project access warning banner */
 .project-warning-banner {
     display: flex;

archive/js/app.js

@@ -272,7 +272,7 @@
     function showHttpErrorState(message) {
         var el = document.getElementById('noDirectoryMessage');
         if (!el) return;
-        var content = el.querySelector('.empty-state-content');
+        var content = el.querySelector('.empty-state__inner');
         if (content) {
             content.innerHTML =
                 '<h2>Could not connect to server</h2>' +
@@ -302,8 +302,8 @@
     function showUnsupportedBrowserMessage() {
         const app = document.getElementById('appContainer');
         app.innerHTML = `
-            <div class="empty-state">
+            <div class="empty-state empty-state--overlay">
-                <div class="empty-state-content">
+                <div class="empty-state__inner empty-state__inner--centered">
                     <h2>Browser Not Supported</h2>
                     <p>This application requires a Chromium-based browser (Chrome, Edge, Brave) with File System Access API support.</p>
                     <p>Please use one of these browsers to access the Archive Browser.</p>

archive/template.html

@@ -237,8 +237,8 @@
         </div>
 
         <!-- No Directory Selected Message -->
-        <div id="noDirectoryMessage" class="empty-state">
+        <div id="noDirectoryMessage" class="empty-state empty-state--overlay">
-            <div class="empty-state-content">
+            <div class="empty-state__inner empty-state__inner--centered">
                 <h2>Welcome to ZDDC Archive</h2>
                 <p>Click <strong>Add Local Directory</strong> to select an archive folder to browse.</p>
                 <p>This browser provides a convenient interface for searching and retrieving files from ZDDC-compliant archives.</p>

browse/css/base.css

@@ -22,35 +22,7 @@ body {
     min-height: 0;
 }
 
-/* Empty / first-paint state */
+/* .empty-state / .empty-state__inner live in shared/base.css. */
-.empty-state {
-    flex: 1;
-    display: flex;
-    align-items: center;
-    justify-content: center;
-    padding: 2rem;
-}
-
-.empty-state__inner {
-    max-width: 640px;
-    color: var(--text-muted);
-    line-height: 1.5;
-}
-
-.empty-state__inner h2 {
-    color: var(--text);
-    margin: 0 0 1rem 0;
-    font-size: 1.5rem;
-}
-
-.empty-state__inner ul {
-    margin: 1rem 0;
-    padding-left: 1.5rem;
-}
-
-.empty-state__inner li {
-    margin: 0.4rem 0;
-}
 
 /* .hidden lives in shared/base.css; no per-tool override needed. */
 

classifier/css/layout.css

@@ -1,46 +1,8 @@
 /* Classifier layout — tokens from shared/base.css */
 
-/* Empty State — positioned below the app header */
+/* .empty-state / .empty-state__inner / .welcome-list live in
-.empty-state {
+   shared/base.css. Classifier keeps the .drag-over modifier locally
-    position: absolute;
+   because it's the only tool whose empty state is a drop target. */
-    top: 50px; /* clear the header */
-    left: 0;
-    right: 0;
-    bottom: 0;
-    display: flex;
-    align-items: center;
-    justify-content: center;
-    background: var(--bg);
-    z-index: 10;
-}
-
-.empty-state-content {
-    text-align: center;
-    max-width: 500px;
-    padding: 2rem;
-}
-
-.empty-state-content h2 {
-    color: var(--text);
-    margin-bottom: 1rem;
-}
-
-.empty-state-content p {
-    margin-bottom: 1rem;
-    color: var(--text-muted);
-}
-
-.empty-state-content .note {
-    font-size: 0.85rem;
-    font-style: italic;
-}
-
-.welcome-list {
-    text-align: left;
-    margin: 0.5rem auto;
-    max-width: 400px;
-}
-
 .empty-state.drag-over {
     background: var(--primary-light);
     outline: 2px dashed var(--primary);

classifier/template.html

@@ -129,8 +129,8 @@
             </div>
 
             <!-- Empty State — shown until a directory is selected -->
-            <div id="welcomeScreen" class="empty-state">
+            <div id="welcomeScreen" class="empty-state empty-state--overlay">
-                <div class="empty-state-content">
+                <div class="empty-state__inner empty-state__inner--centered">
                     <h2>ZDDC Classifier</h2>
                     <p>Rename a folder of files to ZDDC format using a spreadsheet interface.</p>
                     <p>Open a directory, fill in tracking number, revision, status, and title for each file, then save — the files are renamed on disk.</p>

shared/base.css

@@ -349,7 +349,83 @@ a:hover {
     font-size: 1.1rem;
 }
 
-/* Toast CSS lives in classifier/css/base.css — only that tool uses toasts. */
+/* Toast CSS lives in shared/toast.css; loaded by every tool's build. */
+
+/* ── Empty state ──────────────────────────────────────────────────────────── */
+/* The "nothing's loaded yet" screen. By default, centers its inner
+   content in whatever space the parent gives it (works inside a flex
+   column). Tools that need to overlay an existing layout (archive,
+   classifier) add .empty-state--overlay; the screen pins below the
+   app header and on top of whatever underlying layout already exists.
+   Inner content uses BEM-ish .empty-state__inner with two variants:
+   plain (left-aligned, doc-style) and --centered (centered card). */
+
+.empty-state {
+    flex: 1;
+    display: flex;
+    align-items: center;
+    justify-content: center;
+    padding: 2rem;
+    background: var(--bg);
+}
+
+.empty-state--overlay {
+    position: absolute;
+    top: 50px; /* clear the app-header */
+    left: 0;
+    right: 0;
+    bottom: 0;
+    z-index: 10;
+    flex: none;
+}
+
+.empty-state__inner {
+    max-width: 640px;
+    color: var(--text-muted);
+    line-height: 1.5;
+}
+
+.empty-state__inner h2 {
+    color: var(--text);
+    margin: 0 0 1rem;
+    font-size: 1.5rem;
+}
+
+.empty-state__inner p {
+    margin-bottom: 1rem;
+}
+
+.empty-state__inner ul,
+.empty-state__inner ol {
+    margin: 1rem 0;
+    padding-left: 1.5rem;
+}
+
+.empty-state__inner li {
+    margin: 0.4rem 0;
+}
+
+.empty-state__inner .note {
+    font-size: 0.85rem;
+    font-style: italic;
+}
+
+/* Centered variant: tighter max-width + centered text. Used by tools
+   whose empty-state reads as a "welcome card" (archive, classifier)
+   rather than a doc-style page (browse). */
+.empty-state__inner--centered {
+    max-width: 500px;
+    text-align: center;
+    padding: 2rem;
+}
+
+/* Bullet list inside an empty-state — keep the bullets left-aligned
+   even when the surrounding card is centered. */
+.welcome-list {
+    text-align: left;
+    margin: 0.5rem auto;
+    max-width: 400px;
+}
 
 /* ── Theme and help icon buttons ─────────────────────────────────────────── */
 #theme-btn,