mdb-ui-kit/sass/_inputs.scss

fieldset[disabled] .form-control, .form-control-wrapper .form-control, .form-control {
    &, &:focus, &.focus {
        &:not(textarea):not(select) {
            height: 28px;
        }
        padding: 0;
        float: none;
        border: 0;
        box-shadow: none;
        border-radius: 0;
        background: transparent;
        border-bottom: 1px solid #757575;
        &:disabled {
            border-style: dashed;
        }
    }
}
select.form-control {
    height: 23px;
}
select[multiple].form-control {
    &, &:focus, &.focus {
        height: 85px;
    }
}

.form-control-wrapper {
    position: relative;

    .form-control:focus, .form-control.focus {
        outline: none;
    }

    .floating-label {
        color: #7E7E7E;
        font-size: 14px;
        position: absolute;
        pointer-events: none;
        left: 0px;
        top: 5px;
        transition: 0.2s ease all;
        opacity: 0;
    }
    .form-control:not(.empty) ~ .floating-label {
        top: -10px;
        font-size: 10px;
        opacity: 1;
    }
    .form-control:focus:invalid ~ .floating-label, .form-control.focus:invalid ~ .floating-label {
        color: $input-danger;
    }
    .form-control:focus ~ .material-input:after, .form-control.focus ~ .material-input:after {
        background-color: $input-default;
    }
    .form-control:focus:invalid ~ .material-input, .form-control.focus:invalid ~ .material-input {
        &:before, &:after  {
            background-color: $input-danger;
        }
    }
    .form-control.empty ~ .floating-label {
        opacity: 1;
    }
    .material-input:before {
        position: absolute;
        content: "";
        width: 100%;
        left: 0;
        height: 2px;
        background-color: $input-default;
        bottom: -1px;
        transform: scaleX(0);
        transition: transform 0s;
    }
    .form-control:focus  ~ .material-input:before, .form-control.focus  ~ .material-input:before {
        transform: scaleX(1);
        transition: transform 0.2s ease-out;
    }
    .material-input:after {
        content: "";
        position: absolute;
        height: 18px;
        width: 100px;
        margin-top: -1px;
        top: 7px;
        left: 0;
        pointer-events: none;
        opacity: 0.9;
        transform-origin: left;
    }
    .input-lg ~ .material-input:after {
        height: 26px;
    }
    textarea { resize: none; }
    textarea ~ .form-control-highlight {
        margin-top: -11px;
    }

    /* active state */
    .form-control:focus ~ .material-input:after, .form-control.focus ~ .material-input:after {
        animation: input-highlight 0.3s ease;
        animation-fill-mode: forwards;
        opacity: 0;
    }

    select ~ .material-input:after {
        display: none;
    }

}

.form-group {
    &.has-warning {
        .material-input:before, input.form-control:focus ~ .material-input:after, input.form-control.focus ~ .material-input:after {
            background: $input-warning;
        }
        .control-label, input.form-control:not(.empty) ~ .floating-label {
            color: $input-warning;
        }
    }
    &.has-error {
        .material-input:before, input.form-control:focus ~ .material-input:after, input.form-control.focus ~ .material-input:after {
            background: $input-danger;
        }
        .control-label, input.form-control:not(.empty) ~ .floating-label {
            color: $input-danger;
        }
    }
    &.has-success {
        .material-input:before, input.form-control:focus ~ .material-input:after, input.form-control.focus ~ .material-input:after {
            background: $input-success;
        }
        .control-label, input.form-control:not(.empty) ~ .floating-label {
            color: $input-success;
        }
    }
    &.has-info {
        .material-input:before, input.form-control:focus ~ .material-input:after, input.form-control.focus ~ .material-input:after {
            background: $input-info;
        }
        .control-label, input.form-control:not(.empty) ~ .floating-label {
            color: $input-info;
        }
    }
    //.variations(#{" .material-input:before"}, background-color, $indigo);
    //.variations(#{" input.form-control:focus ~ .material-input:after"}, background-color, $indigo);
    //.variations(#{" input.form-control.focus ~ .material-input:after"}, background-color, $indigo);
    //.variations(#{" .control-label"}, color, $lightbg-text);
    //.variations(#{" input.form-control:not(.empty) ~ .floating-label"}, color, $indigo);

}

.input-group {
    .form-control-wrapper {
        .form-control {
            float: none;
        }
        margin-right: 5px;
        margin-left: 5px;
        bottom: -10px;
    }
    .input-group-addon {
        border: 0;
    }
    .input-group-btn .btn {
        border-radius: 4px;
    }
}

select.form-control {
    border: 0;
    box-shadow: none;
    border-bottom: 1px solid #757575;
    border-radius: 0;
    &:focus, &.focus {
        box-shadow: none;
        border-color: #757575;
    }
}


@mixin keyframe-input-highlight(){
    0% {
        left: 20%;
        transform: scaleX(20%);
    }
    99% {
        transform: scaleX(0);
        left: 0;
        opacity: 1;
    }
    100% {
        opacity: 0;
    }
}

@keyframes input-highlight {
    @include keyframe-input-highlight()
}


// Input files (kinda hack)
.form-control-wrapper input[type=file] {
    opacity: 0;
    position: absolute;
    top: 0;
    right: 0;
    bottom: 0;
    left: 0;
    width: 100%;
    height: 100%;
    z-index: 100;
}