Text areas have the option to automatically display the remaining number of characters.  This number will automatically decrease as the user types.
In the DataPage wizard, after you’ve selected Text Area from the Form Elements dropdown, you will see the Field Options section below.  The last two options allow you to configure the remaining characters display.

You can set the Max characters to any number you would like as long as it is less than or equal to the available characters in that field’s data type.

Styling the Field Help

The remaining characters text is considered “Field Help” and is customizable using the Style Wizard.  In the Caspio Explorer window, go to the Styles view.  Select the Style you are using for your DataPage and click Edit.  Proceed to the Settings screen.  Under the Forms/Details group, locate the Fields subheading.  Field Help is the third Element Type.  You can use the controls to change the font style and layout of that help field.