It’s been kind of bugging me for a while: The triangle icon before the title on the Genesis Accordion Block (formerly Atomic Blocks Accordion Block).

Today I searched for a solution and found one. Thought I share the code here for future reference and for everyone who happen to stumble upon this post. Here is the CSS snippet that makes the triangle go away.
.gb-block-accordion details summary::-webkit-details-marker {
display:none;
}
I found the solution on Stack Overflow after a thread on the Atomic Blocks forum learned me that this triangle was browser generated.
Other styling adjustments
To make it fit my need, I made a few more styling adjustments. I changed the background color, added a box shadow and applied some Font Awesome icons to replace the triangle. This is the result.
Some Random Title in the Accordion Block
This is how the accordion looks now.
Here is a snippet of the CSS (click here for the raw snippet).