Fix frame border issue

[5yutan5]

This PR fix the frame border issue as discussed in #54.
This fix will only work if QWidget is entered into QScrollArea.setWidget().
This is because it forces the background of a child widget of QScrollArea to be transparent, which may cause the color of widgets whose background color is different from the base color, such as QPushButtoon and QTableView, to disappear.

• Fixed a bug where widgets in scroll area would hide a part of scroll area border when padding of scroll area is 0.

[codecov]

Codecov Report

Merging #57 (c538cb2) into main (25e60f9) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##              main       #57   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           19        19           
  Lines          585       585           
=========================================
  Hits           585       585           

Impacted Files	Coverage Δ
qdarktheme/themes/dark/rc_icons.py	100.00% <ø> (ø)
qdarktheme/themes/dark/stylesheet.py	100.00% <ø> (ø)
qdarktheme/themes/light/rc_icons.py	100.00% <ø> (ø)
qdarktheme/themes/light/stylesheet.py	100.00% <ø> (ø)

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