Шаблон:SwearingWarning/styles.css

.message-box {
  margin-bottom: 6px;
  background: rgba(20,20,20,0.12);
  border-radius: 5px;
  overflow: hidden;
  display: grid;
  border: 1px solid #000;
  align-items: center;
}
.message-box::before {
  content: "";
  display: block;
  width: 6px;
  height: 100%;
}
.message-box.warning::before {
  background: yellow;
}