I'm able to change the button's background color using the Color
property on the component, but I don't see a property to change the border color.
You can see here that the button has a border, but I'm not sure how to change the border color in Delphi:
There doesn't seem to be a property to change this in design-time, So you'll have to change it dynamically during run-time.
In the OnCreate
event of the form, you can write:
WebButton1.ElementHandle.style.setProperty('border-color', 'red');
The first parameter, you pass in the border-color
CSS property, and the second parameter you pass in the HTML Color: