Pillarbox’s appearance is fully customizable. Background color, font color, font size, font family, etc can be customized from the extension option menu (Tools – Extension – Pillarbox – Options). However, basic CSS knowledge required.
Note: Though it saves the text locally, it cannot be saved to a file (it will be added as soon as Chrome makes it possible). Therefore, after finishing your writing you need to copy and paste them into a document editor. You can install Pillarbox from Chrome Web Store
