topbar.js binds click handlers to every .dark-toggle, including the settings one; settings.js then also wired a delegation that re-clicked the topbar button, so each click flipped dark mode twice (net no-op). Mark buttons as wired in topbar.js and only add a fallback handler in settings.js when topbar.js did not run. CSS: center the toggle horizontally under the Settings title with auto margins, matching .settings-body padding. Closes #197