resolved other components popping up the date picker by adding z-index

[Chandrachur67]

1. while using the date picker, hovering over card components was causing cards popping up the data picker. I have added a z-index = 10 to the date picker component so that the cards don't pop up that.
2. Due to absolute positioning the date picker and guest selector were separating out. I have fixed that problem also.

before

after

[Chandrachur67]

If someone having problem to run this in local system.

1. npm install
2. npm i @material-ui/core
3. npm i @material-ui/icons
4. npm start