.circle {
    background-color: #ccc;
    border-radius: 50%;
    height: 2.5rem;
    text-align: center;
    width: 2.5rem;
}

.initials {
    font-size: calc(2.5rem / 2); /* 50% of parent */
    line-height: 1;
    position: relative;
    top: calc(2.5rem / 4); /* 25% of parent */
}