How can I add a bottom border to the app title?

The app does not have an option to add a bottom border to the title out-of-the-box, but you can use the additional styles field to create it with a couple of CSS rules.

Over the Additional styles preference, you can type there any CSS rules using JSON format.

The following is the code for a simple black border:

{"border-bottom":"solid 1px black"}

You can replace1px by the desired width of the border, such as 2px or 6px.

You can replace black by the desired color of the border, such as red or yellow.

Furthermore, you can find a lot of supported color names at https://www.w3schools.com/colors/colors_names.asp

For example, the following code would display a thick brown border:

{"border-bottom":"solid 3px brown"}

Depending on your theme default styles, you can also play with the title height and bottom margin to make it look better, such as the following code:

{"border-bottom":"solid 1px red", "line-height":"40px", "margin-bottom":"20px"}