Battlestar Galactica Corners

For the BSG corners on my about me picture, inspired by this codepen, in Firefox I used the CSS clip-path (MDN), disabled the body background image of chrome://global/skin/media/imagedoc-darknoise.png, screenshotted it then used the macOS Preview magic tool to cut out the background to get the clear alpha.

clip-path: polygon(
     20% 0, 80% 0, 
     100% 15%, 100% 85%, 
     80% 100%, 20% 100%, 
     0% 85%, 0 15%
 )