Black lines appear at the top of the custom dialog box, and the bottom is normal. How can this problem be solved? Please kindly enlighten me ~~

In my custom dialog box, the style is the border of the rounded corner. At the beginning, the corner is black and angular, and setbackgrounddrawableresource (Android. r. color. transparent); it does improve, but when the background of the activity is not black (the border line should be hidden when it is black ), A black border line is displayed at the top of the dialog box. I have read the problem that layout is the most external layout of the dialog box, but setting its background to transparent is ineffective... Please kindly enlighten me ~~