Add this code to the Custom CSS field on the More tab of your Facebook Feed widget’s settings:
.eapps-facebook-feed-inner{
border-radius: 0px !important;
}
.eapps-facebook-feed-header{ border-radius: 0; }
img[src*='data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAwAAAAKCAYAAACALL/6AAAAGXRFWHRTb2Z0d2FyZQBBZG9iZSBJbWFnZVJlYWR5ccllPAAAANZJREFUeNp80D8OAUEUx/FZNlQqJAqR+HMDGjQKV5CIRqV1AldQUDiCRtiERqNUiwQFWRqNDQ2dCL4jQyZLvOQzL9n9vZnZNZK9R0oIcbBLxkVoxfMMrY04RrBgeljKGBOIaWG/CmURQQ1DpE25O3JYEGzRu/CqoF4OOvKEDU4IoIEVZuK71lzbkQMhBF0vzR8DS7nIgQHkVa7if1mvAY650/fw/QlPyU3eJ8hqoq4G3XVE9XNX/kyenkABUVd4jgq72/rH7VBEGFuc1Z/rS4Rv+g5PAQYAIPI34+MZpFcAAAAASUVORK5CYII='] {
display: none;
}
.eui-popover-content-item:nth-child(2) .eui-popover-content-item-icon::before {
content: '';
width: 12px;
height: 12px;
background-size: cover;
background-image: url('data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAABAAAAAQCAQAAAC1+jfqAAAAyElEQVR42n3RsQpBARSH8e+prhIRspgVCylKSXkCZVEGiwcw3IGSzIqyKLvBKMpgESVCruPUFV2u2zec4f/bDoCP5J989iweGagTdvS0AY/3cGaIaEkbWERpUqT1mi1SDqBtSHAhxBzRKrQRB9D61FkS4EqTGvIDtCwzTGLkEXdwIMSRNKM/QDPJKfNzcAdbwhToMiXjBk7EmXMjwooqnW9w1ztGtAUxLorXTlDCRF61KNMgiPUBeybIuwcDetrOBob3s7zfbcATzB64T8N4IH0AAAAASUVORK5CYII=');
}
.eui-popover-content-item:nth-child(2) .eui-popover-content-item-title {
visibility: hidden;
position: relative;
}
.eui-popover-content-item:nth-child(2) .eui-popover-content-item-title::before {
content: "Share on X";
visibility: visible;
position: absolute;
top: 0;
left: 0;
}