How Can I Add A Border And Drop Shadow To My Embedded Calendar Block

Hey, I recently added this Availability Calendar onto my website, which is hosted by a booking platform outside of squarespace.

I entered the embedded code to get the calendar on my site, but I was wondering if I could add a black outline, and maybe a drop shadow around it. 

I'm stuck and assuming that it has to be displayed the way it is, since it's coming from the booking site that I am using.

This is the website: PerfectCaptureBooth.com 
Password : 2926

It's right on the home page. and This is the block ID:

#block-yui_3_17_2_1_1690939779928_4739

I was thinking it would be as easy as doing :

#block-yui_3_17_2_1_1690939779928_4739 {
  filter: drop-shadow(5px 5px 8px #000000);
}

But I guess that doesn't work.
Any help would be appreciated!

Hi,

Can you share link to page where you added it? We can check easier