It would be good to add some visual highlights to certain key sections

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I see that besides some user interface issues like this, everything else seems more user-friendly compared to previous versions. If possible, it would be good to add some visual highlights to certain key sections.

For example, for the minimum/maximum BTC amount fields, as the user is inputting values, have an error message pop up right at the point where the number becomes invalid. Also, the Preview button should automatically light up if the input data is valid, without requiring the user to click outside or press enter.