Black Border in External Monitor OSX El Capitan 1920 x 1080 I've got this issue with OSX El Capitan. My existing monitor show black border in resolution 1920 x 1080. The black border is shown only on left side of monitor. This never happen previously in Yosemite. 

What I've tried but didn't work: 


set resolution in safe mode
unplug and plug again my mini to VGA cable
Restart
play with my monitor setting (reset setting)


Here is the screenshot: 



Thank you for your help
Same problem with my Acer monitor. I've researched a lot online. Next few days my ordered VGA-DVId will test my last resort. So I suggest you might change your monitor's input to DVI. This solved the issue for me.