.input .slds-input_faux{
    border-top: none;
    border-left: none;
    border-right: none;
    border-radius: 0;
}

.input .slds-input {
    font-size: 1rem;
    border-top: none;
    border-left: none;
    border-right: none;
    border-radius: 0;
}