To design a GUI that supports both desktop and mobile access for HR tools, consider a responsive design that adapts to different screen sizes and devices. Start with a mobile-first approach, designing for mobile devices and then adapting for desktop devices. Use consistent navigation patterns across both desktop and mobile devices, and ensure that buttons and interactive elements are large enough for fingers to tap on mobile devices.

Take advantage of desktop-specific features like keyboard shortcuts and drag-and-drop functionality, while leveraging mobile-specific features like GPS, camera, and push notifications. Use progressive disclosure to hide or reveal content and features based on screen size and device.

Test the GUI on various devices and iterate on the design to ensure a seamless experience. Ensure cross-browser compatibility and incorporate accessibility features like screen reader support and high contrast mode.

By following these guidelines, you can create a GUI that provides an optimal experience for both desktop and mobile users, making HR tools accessible and user-friendly across devices. The design should be flexible and adaptable, allowing users to easily switch between devices and pick up where they left off.