diff --git a/src-tauri/src/git.rs b/src-tauri/src/git.rs
index ea969e1..8bbfaae 100644
--- a/src-tauri/src/git.rs
+++ b/src-tauri/src/git.rs
@@ -836,7 +836,13 @@ pub fn set_branch_upstream(
             )?;
         }
         None => {
-            run_git(&repo, ["branch", "--unset-upstream", branch.as_str()])?;
+            // Saving sync settings with "No upstream" must be idempotent. Git
+            // exits with a fatal error when --unset-upstream is used on a
+            // branch that never had tracking information, which is the normal
+            // state immediately after adding the first remote.
+            if git_config_value(&repo, &format!("branch.{branch}.merge")).is_some() {
+                run_git(&repo, ["branch", "--unset-upstream", branch.as_str()])?;
+            }
         }
     }
     status_for_repo(&repo)
@@ -7661,6 +7667,25 @@ mod tests {
         assert_eq!(remote.upstream, None);
     }
 
+    #[test]
+    fn clearing_an_unconfigured_upstream_is_a_noop() {
+        let repo = init_temp_repo("unset_missing_upstream");
+        commit_initial_file(&repo.path);
+        let branch = git_output_test(&repo.path, ["branch", "--show-current"]);
+        run_git_test(&repo.path, ["remote", "add", "origin", "."]);
+
+        let status = set_branch_upstream(
+            repo.path.to_string_lossy().to_string(),
+            branch.clone(),
+            None,
+        )
+        .expect("saving an empty upstream should not fail");
+
+        assert_eq!(status.current_branch.as_deref(), Some(branch.as_str()));
+        assert_eq!(status.upstream, None);
+        assert!(git_config_value(&repo.path, &format!("branch.{branch}.merge")).is_none());
+    }
+
     #[test]
     fn commit_notes_can_be_created_updated_and_deleted_without_changing_commit() {
         let repo = init_temp_repo("commit_notes_crud");
diff --git a/src/app.css b/src/app.css
index 6e725fd..356f8ed 100644
--- a/src/app.css
+++ b/src/app.css
@@ -8672,3 +8672,169 @@ input:focus, textarea:focus, select:focus { box-shadow: 0 0 0 3px color-mix(in s
   .branch-filter-summary { align-items: stretch; flex-direction: column; }
   .branch-filter-actions { display: grid; grid-template-columns: repeat(3, minmax(0, 1fr)); }
 }
+
+/* Authentication and token dialogs ------------------------------------
+   Keep credentials, access tokens and API-key forms on the active theme
+   instead of the legacy violet/black palette. */
+.cred-card,
+:root[data-theme="light"] .cred-card {
+  border-color: var(--color-border-input);
+  background: var(--app-dialog-bg);
+  box-shadow: var(--app-dialog-shadow);
+}
+
+.cred-hero,
+:root[data-theme="light"] .cred-hero {
+  border-bottom-color: var(--color-border);
+  background:
+    radial-gradient(circle at 8% 0%, color-mix(in srgb, var(--color-accent) 14%, transparent), transparent 44%),
+    var(--app-dialog-chrome);
+}
+
+.cred-hero-icon,
+:root[data-theme="light"] .cred-hero-icon {
+  border-color: color-mix(in srgb, var(--color-accent) 42%, var(--color-border));
+  color: var(--color-accent);
+  background: color-mix(in srgb, var(--color-accent) 12%, var(--color-surface-raised));
+  box-shadow: 0 10px 24px color-mix(in srgb, var(--color-accent) 18%, transparent);
+}
+
+.cred-hero-label,
+:root[data-theme="light"] .cred-hero-label {
+  color: var(--color-accent);
+}
+
+.cred-hero-title,
+:root[data-theme="light"] .cred-hero-title {
+  color: var(--color-ink);
+}
+
+.cred-hero-copy,
+:root[data-theme="light"] .cred-hero-copy {
+  color: var(--color-ink-muted);
+}
+
+.cred-security-note,
+:root[data-theme="light"] .cred-security-note {
+  border-color: color-mix(in srgb, var(--color-accent) 32%, var(--color-border));
+  color: var(--color-ink-muted);
+  background: color-mix(in srgb, var(--color-accent) 8%, var(--color-surface-raised));
+}
+
+.cred-security-note svg,
+:root[data-theme="light"] .cred-security-note svg {
+  color: var(--color-accent);
+}
+
+.cred-close,
+:root[data-theme="light"] .cred-close {
+  border-color: var(--color-border);
+  color: var(--color-ink-faint);
+  background: var(--color-surface-raised);
+}
+
+.cred-close:hover:not(:disabled),
+:root[data-theme="light"] .cred-close:hover:not(:disabled) {
+  border-color: var(--color-border-input);
+  color: var(--color-ink);
+  background: var(--color-surface-hover);
+}
+
+.cred-body,
+:root[data-theme="light"] .cred-body {
+  background: var(--app-dialog-bg);
+}
+
+.cred-segment,
+:root[data-theme="light"] .cred-segment {
+  border-color: var(--color-border);
+  background: var(--color-surface-alt);
+}
+
+.cred-seg-btn,
+:root[data-theme="light"] .cred-seg-btn {
+  color: var(--color-ink-faint);
+}
+
+.cred-seg-btn:hover:not(.active),
+:root[data-theme="light"] .cred-seg-btn:hover:not(.active) {
+  color: var(--color-ink);
+  background: var(--color-surface-hover);
+}
+
+.cred-seg-btn.active,
+:root[data-theme="light"] .cred-seg-btn.active {
+  border-color: color-mix(in srgb, var(--color-accent) 46%, var(--color-border));
+  color: var(--color-ink);
+  background: color-mix(in srgb, var(--color-accent) 12%, var(--color-surface-raised));
+  box-shadow: inset 0 -2px 0 var(--color-accent);
+}
+
+.cred-input input,
+.cred-expiry input[type="date"],
+:root[data-theme="light"] .cred-input input,
+:root[data-theme="light"] .cred-expiry input[type="date"] {
+  border-color: var(--color-border-input);
+  color: var(--color-ink);
+  background: var(--app-input-bg);
+  color-scheme: var(--app-color-scheme);
+}
+
+.cred-input input::placeholder,
+:root[data-theme="light"] .cred-input input::placeholder {
+  color: var(--color-ink-faint);
+  opacity: 0.72;
+}
+
+.cred-token-hint,
+:root[data-theme="light"] .cred-token-hint {
+  border-color: color-mix(in srgb, var(--color-accent) 34%, var(--color-border));
+  color: var(--color-ink-muted);
+  background: color-mix(in srgb, var(--color-accent) 8%, var(--color-surface-dim));
+}
+
+.cred-token-hint code,
+:root[data-theme="light"] .cred-token-hint code {
+  color: var(--color-accent);
+  background: color-mix(in srgb, var(--color-accent) 12%, var(--color-surface-raised));
+}
+
+.cred-footer {
+  border-top-color: var(--color-border-subtle);
+}
+
+.cred-save input[type="checkbox"] {
+  accent-color: var(--color-accent);
+}
+
+.cred-save span {
+  color: var(--color-ink-muted);
+}
+
+.cred-cancel {
+  border-color: var(--color-border);
+  color: var(--color-ink-muted);
+  background: var(--color-surface-raised);
+}
+
+.cred-submit {
+  border-color: color-mix(in srgb, var(--color-accent) 62%, var(--color-border));
+  color: var(--color-surface-solid);
+  background: var(--color-primary-dark);
+  box-shadow: none;
+}
+
+.cred-submit:hover:not(:disabled) {
+  border-color: var(--color-accent);
+  color: var(--color-surface-solid);
+  background: var(--color-primary);
+}
+
+@media (max-width: 560px) {
+  .cred-card { width: calc(100vw - 16px); max-height: calc(100vh - 16px); }
+  .cred-hero { padding: 16px; }
+  .cred-body { padding: 16px; }
+  .cred-security-note { align-items: flex-start; border-radius: 8px; padding-block: 7px; }
+  .cred-footer { align-items: stretch; flex-direction: column; }
+  .cred-btns { display: grid; grid-template-columns: 1fr 1fr; }
+}