A while back I made a donation and received this t-shirt.

There are some problems here.
First, this is supposed to be a code snippet that geeks-in-the-know would recognize as CSS syntax (for adding styles to a webpage.) #000000 is the hex value for the color black. So now you get it.
But… no.
In real CSS, this snippet indicates that you have an element in your HTML with an ID of ‘000000’ which, while technically not illegal, is just a really bad idea.
A more syntactically correct (and semantically sensible) version of this might be:
.lives-matter {
color: #000000;
}
Where the class of your HTML element is ‘lives-matter’ and the statement’s attribute: value pair is, well you get the idea…
That’s a long way to go just to be cute and it’s not even geek-friendly.
Secondly, to people who don’t understand the code (and are maybe not smug jerks), the code might just read as “zero lives matter.”
And finally, is it really a good idea to try and be cute about something this important? Because it seems to me this shirt ends up being more about the person who made it and less about discrimination against people of color.
On the other hand, it could be a good conversation starter and maybe I’m trying to be too proper for my own good.
I don’t think I’m going to wear it if I leave the house, but it does seem pretty good at picking up cat hair.