User:Cyton/vector-2022.css

.cm-mw-matchingbracket
{
    box-shadow:none; /* remove white glow */

    /* four 1px thick gradients */
    background-image: linear-gradient(to right, #444 1px, #999 1px, #999 calc(100% - 1px), #444 calc(100% - 1px)), /* top */
    linear-gradient(#999, transparent, #999), /* right */
    linear-gradient(to right, #444 1px, #999 1px, #999 calc(100% - 1px), #444 calc(100% - 1px)), /* bottom */
    linear-gradient(#999, transparent, #999); /* left */
    
    background-repeat: no-repeat;
    
    /* sizes: top/bottom full width; left/right full height minus top+bottom-corner and minus gap at top/bottom = 1+1+1+1 = 4*/
    background-size: 100% 1px, /* top */
    1px calc(100% - 4px), /* right */
    100% 1px, /* bottom */
    1px calc(100% - 4px);/* left */
    
    background-position: left 0 top 1px, /* top, offset from top = 1*/
    right 0 top 2px, /* right, offset from top + offset from corner = 2*/
    left 0 bottom 1px, /* bottom */
    left 0 top 2px;    /* left */
}