Added Platform CSS feature to Platform Administration. Super admins can now edit global CSS overrides that apply across the entire platform UI. Architecture: (1) DB — added platform_css LONGTEXT column to configurations table. (2) Admin Map — added Platform CSS link under PLATFORM section in dashboard.php. (3) Editor page — /platform/administration/platform_css/ with CodeMirror (CSS mode, blackboard theme), SweetAlert save confirmation, AJAX save to inc/save.php. (4) Global injection — head.php outputs <style id=platform-css-override> after all template CSS, loaded from configurations table. (5) Auth — super_admin only, following existing admin auth pattern (Account->logged + session check). Mirrors existing Website CSS Codes feature architecture.