If you are seeing very large or very small font sizes in CLEO when using FastX, there are two ways to try and address this. Firstly, you can try to adjust the screen resolution in FastX by clicking on the sliders icon in the small options menu that appears when you hover your mouse cursor at the top middle of the browser screen. Alternatively, you can type 'xrandr --dpi 96' in the terminal before starting CLEO.