CSS conflict with plugin on theme

Hi there, I’ve searched all over the web, but couldn’t get a solution to this issue I’m facing.
I’m going to provide links to images to better explain the situation:

I think this may be a js or a css conflict, i will include as much detail as possible:
1: I have a theme on which there are forms.
As seen here: https://i.imgur.com/RN1H4f7.png

2: When a visitor clicks on the date option a drop down calendar should appear.
As seen here: [This is from another website where the same plugin is implemented with another theme] https://i.imgur.com/zRfizEX

3: But, on the website where I have implemented this as seen in number 1, the drop down calendar does not appear.

Help is greatly appreciated!
If needed css codes, I’ll provide them.
Thank you so much

[Moderator Note: Please ensure that you are embedding links correctly in your posts.]

Thank you Moderator, I was about to edit it.

Update:
I have disabled all plugins and that is still not solving the issue.