Added modals for popups, and fixed root-level bug.

Frontend/src/Styles/Theme.css

@@ -784,6 +784,38 @@ img,
   font-size: 13px;
 }
 
+.ErrorToast {
+  position: fixed;
+  bottom: calc(20px + env(safe-area-inset-bottom, 0px));
+  left: 50%;
+  transform: translateX(-50%);
+  display: flex;
+  align-items: center;
+  gap: 12px;
+  max-width: 480px;
+  padding: 10px 14px;
+  background: var(--Surface);
+  border: 1px solid var(--Red);
+  border-radius: 6px;
+  color: var(--Text);
+  font-size: 13px;
+  z-index: 200;
+}
+
+.ErrorToastClose {
+  background: none;
+  border: none;
+  color: var(--TextMuted);
+  cursor: pointer;
+  font-family: inherit;
+  font-size: 13px;
+  padding: 0;
+}
+
+.ErrorToastClose:hover {
+  color: var(--Text);
+}
+
 .SettingsHint {
   color: var(--TextMuted);
   font-size: 12px;