AMAYA 9.52 WINDOW FRAME

there is an orange window frame on the browser
1] why does it change color when hovered
2] why is there a gap in the bottom left corner
3] can color be controlled from style sheer or is there
another setting for users to cusomize this ?feature? 

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John Russell, VE3LL@COGECO.CA
http://home.cogeco.ca/~ve3ll
http://home.cogeco.ca/~trains
http://home.cogeco.ca/~cipher