.form-control.is-invalid {
    border: 2px solid #DC3545;
}

#diasSemanaError.invalid-feedback {
    display: block !important;
    width: 100%;
    margin-top: 0.25rem;
    font-size: 0.875em;
    color: #DC3545;
    font-weight: bold;
}

.is-invalid ~ .invalid-feedback {
    display: block;
    font-weight: bold;
}

.invalid-feedback {
    display: block;
    width: 100%;
    margin-top: 0.25rem;
    font-weight: bold !important;
    color: #DC3545 !important;
}

.input-group {
    display: flex;
    flex-wrap: nowrap;
    align-items: stretch;
}

    .input-group .form-control {
        flex: 1 1 auto;
        min-width: 0;
    }

    .input-group .input-group-text {
        align-items: center;
        display: flex;
    }