Stretch the date picker to full width

I am using react-datepicker.

<div className="context-param context-param-line">
    <div className="context-param-name">Check In </div>
    <div className="context-param-value">

The existing styles are:

.context-param-line {
    flex: 1;
    margin: 10px;
    display: flex;
    flex-direction: column;
    align-items: center;

.context-param-name {
    font-weight: 200;
    text-align: center;
    margin-bottom: 5px;
    font-size: 16px;

.context-param-value {
    color: #888;
    font-size: 16px;

I want to stretch the datepicker to the full width of the container. Right now, the width is hard-coded to 147px. Also, I want to adjust the z-index of the date picker. I tried various CSS options but could not get it to work. Does anyone know the exact CSS to fix the width to the parent container? Thanks.