If, instead of a solid colour, you wish to make the background of your Countdown Timer Bar a gradient, you can do so with a few small edits.
This isn't an official feature, but it can be done.
If you are on the premium plan, in the bottom section of the bar configuration, you can paste this code into the code box:
background-image: linear-gradient(to right, #E86712 , #f0d800);
background-color: rgba(0, 0, 0, 0) !important;
Alternatively, if you are not on the premium plan, you can add the code to the message directly, like so:
The result will be the same:
From here, you can replace the colour codes. #E86712 and #f0d800 are the codes that refer to the beginning colour and ending colour.
You can use this tool to help you find the codes to the colours you wish to use.
You could also place the code inside the theme.liquid <head> section. This can be handy if you have many bars and want all to have the same gradient.