Trying to get header logo on one page to be a different colour

Hi, I need a different/lighter version of my header logo to appear on the black background of my About page. I pasted in some CSS which was working for a while, but now it isn't and it's saying 'Syntax Error On Line 1'.

Any help would be very much appreciated please. Here's the code I used:

</style>
.header-title-logo a {
  content: url("https://static1.squarespace.com/static/616448878db4ba5c32bc74c2/t/63e101ed9e6cd3537d676158/1675690477827/Z_Mark_Logo_v3.png");
  }
</style>

Thank you