body {
    background: var(--bs-dark);
}

.otp-form .otp-field {
    display: inline-block;
    width: 4rem;
    height: 3rem;
    font-size: 2rem;
    line-height: 4rem;
    text-align: center;
    border: none;
    border-bottom: 2px solid var(--bs-secondary);
    outline: none;
}

    .otp-form .otp-field:focus {
        border-bottom-color: var(--bs-dark);
    }