sp-codes.de/src/scss/icons.scss

.si, .si::before {
  display: inline-block;
  margin: 0 8px;
  width: 4em;
  height: 4em;
  line-height: 1;
  box-sizing: border-box;
}

@media (max-width: 767.98px) {
  .si, .si::before {
    margin: 0 4px;
    width: 2em;
    height: 2em;
  }
}

.h2si, .h2si::before {
  margin: 0;
  width: 30px;
  height: 24px;
}

@mixin svg-icon($name) {
  .si-#{$name}::before {
    content: '\200b';
    background-image: url("../img/#{$name}-white.svg");
    background-repeat: no-repeat;
    background-position: center;
  }
}

@include svg-icon('matrix');
@include svg-icon('gitea');
@include svg-icon('xmpp');
@include svg-icon('threema');
@include svg-icon('opencollective');