fix(ui): contain email split divider (#1194)

static/style.css

@@ -14577,6 +14577,7 @@ body:has(.doc-version-panel:not(.hidden)) .hamburger-btn {
     z-index: 260 !important;
     margin-top: 0 !important;
     transform: none !important;
+    border-left: none !important;
   }
 }
 

tests/test_email_split_border_css.py

@@ -0,0 +1,18 @@
+from pathlib import Path
+
+
+CSS = (Path(__file__).parents[1] / "static" / "style.css").read_text(encoding="utf-8")
+
+
+def _rule(selector: str) -> str:
+    return CSS.split(selector, 1)[1].split("}", 1)[0]
+
+
+def test_email_split_document_pane_drops_duplicate_border():
+    rule = _rule("body.email-doc-split-active.doc-view .doc-editor-pane {")
+    assert "border-left: none !important;" in rule
+
+
+def test_email_split_panel_keeps_visible_seam():
+    rule = _rule(".modal.email-snap-left .modal-content {")
+    assert "border-right: 1px solid var(--border);" in rule