select2/select2-bootstrap.css

.form-control .select2-choice {
    border: 0;
    border-radius: 2px;
}

.form-control .select2-choice .select2-arrow {
    border-radius: 0 2px 2px 0;   
}

.form-control.select2-container {
    height: auto !important;
    padding: 0px;
}

.form-control.select2-container.select2-dropdown-open {
    border-color: #5897FB;
    border-radius: 3px 3px 0 0;
}

.form-control .select2-container.select2-dropdown-open .select2-choices {
    border-radius: 3px 3px 0 0;
}

.form-control.select2-container .select2-choices {
    border: 0 !important;
    border-radius: 3px;
}