Drop cap for a specific paragraph not working when block ID added to CSS

I'm trying to target specific block IDs so I can add a drop capital letter to the first letter of specific paragraphs.  This code works fine BEFORE I add the block ID -- it applies the drop cap to ALL paragraphs.  So what am I messing up when I add the block ID?

//Drop Case Letters - not working when block ID is added//
#block-yui_3_17_2_1_1711480533458_360782:first-letter{
 font-weight: bolder;
 display: block;
 float: left;
 margin-top: 1rem;
 margin-bottom: 0rem;
 margin-right: 3px;
 font-size: 4rem; 
}

The screenshot below is from the "Joie de Vivre" page.

@tuanphan You rock. Thank you!