Adapt extension to the nested replies feature

Some features didn't work correctly with threads which included nested
replies, so this CL addresses those issues.

Fixed: twpowertools:128, twpowertools:133, twpowertools:134
Change-Id: Id1edaa501cdf904326749bf558837938f45f2500
diff --git a/src/static/css/ccdarktheme.css b/src/static/css/ccdarktheme.css
index 9bf1351..e912a8c 100644
--- a/src/static/css/ccdarktheme.css
+++ b/src/static/css/ccdarktheme.css
@@ -1751,6 +1751,16 @@
   color: var(--TWPT-interop-secondary-text);
 }
 
+.scTailwindThreadMessagegapdivider {
+  background: var(--TWPT-interop-subtle-border);
+}
+
+.scTailwindThreadMessagegapbutton {
+  background: #1f1f1f;
+  border: 1px solid var(--TWPT-interop-subtle-border);
+  color: var(--TWPT-interop-secondary-text);
+}
+
 .scTailwindThreadPesignupdialogclose-button-row button {
   color: #fff;
 }