forgetest: theme.css from forgectrl at its new pin

The pin to forgectrl 55bfae9 (9f7744b) brought theme.css's extension
rules - the advisory's document box and the capability lists (cf140a9),
and a package's frame (7543eea) - that forgetest's shared copy did not
have, so check-ui-vendor failed forgetest-ci. The copy is forgectrl's file
at 55bfae9, byte for byte; the rules only add classes forgetest's page
does not use.

Proof: scripts/check-ui-vendor.py reports the shared UI files identical
at the pinned revision.

forgetest/forgetest/ui/theme.css

@@ -451,6 +451,23 @@ footer a {
   font-size: 11.5px;
   margin-left: 2px;
 }
+.extadvdoc {
+  max-height: 22rem;
+  overflow-y: auto;
+  margin-bottom: 0.5rem;
+}
+.extadvdoc h1,
+.extadvdoc h2 {
+  font-size: 1rem;
+  margin: 0.6rem 0 0.3rem;
+}
+.extcaps {
+  margin: 0.2rem 0 0.2rem 1.1rem;
+  padding: 0;
+}
+.extcaps li {
+  margin: 0;
+}
 .hint {
   color: var(--og-dim);
   font-size: 12.5px;
@@ -798,3 +815,9 @@ footer a {
   min-height: 16px;
   text-align: right;
 }
+
+/* A package's interface: the label is the panel's, the frame is the
+   package's, and the frame is given a size rather than taking one. */
+#extframe { margin-top: 0.6rem; }
+.extframe-label { padding: 0.3rem 0; }
+.extframe { width: 100%; height: 360px; border: 1px solid #444; background: #fff; }