.avatar-letter {
  /* Force flex container */
  display: flex !important;         /* !important to override phpBB if needed */
  align-items: center !important;   /* vertical center */
  justify-content: center !important; /* horizontal center */
  
  /* Fixed size for the avatar */
  width: 200px;
  height: 100px;

  /* Grey box styles */
  background-color: transparent;
  border: 1px solid transparent;
  border-radius: 6px;

  /* Text styles */
  color: #fff;
  font-size: 22px;            /* pick a comfortable size for 6 digits */
  font-weight: bold;
  text-transform: uppercase;
  text-align: center;

  /* Prevent wrapping if you want a single line */
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
  
  /* Ensure line-height doesn’t push content up or down */
  line-height: normal !important;
}

/* If phpBB applies .avatar to the same element, override that as well */
.avatar.avatar-letter {
  display: flex !important;
  align-items: center !important;
  justify-content: center !important;
  vertical-align: middle !important;
}