I have a react modal and inside it I have react-select. How can I make select overlay the modal because some of my options in the botttom of modal did not appear ?

I tried z-index but it did not work.
<MainSelect
className="select"
id={name}
isMulti
isRtl={!locale.ltr}
components={{ Option: OptionComponent }}
styles={this.customStyles}
theme={this.customTheme}
options={options}
value={value}
placeholder={placeholder}
onChange={this.handleChange}
onBlur={formik.onBlur}
onMenuOpen={() => {
if (setScroll) setScroll();
this.props.formik.setStatus("onMenuOpen");
}}
/>