<p dir="auto">When implementing modal, the backdrop opacity was set to 1. I checked the css and found that the following</p>
<div class="snippet-clipboard-content notranslate position-relative overflow-auto" data-snippet-clipboard-copy-content=".modal-backdrop.fade {
  opacity: 0;
  filter: alpha(opacity=0);
}
.modal-backdrop.in {
  opacity: 0.5;
  filter: alpha(opacity=50);
}"><pre class="notranslate"><code class="notranslate">.modal-backdrop.fade {
  opacity: 0;
  filter: alpha(opacity=0);
}
.modal-backdrop.in {
  opacity: 0.5;
  filter: alpha(opacity=50);
}
</code></pre></div>
<p dir="auto">...was being overridden by</p>
<div class="snippet-clipboard-content notranslate position-relative overflow-auto" data-snippet-clipboard-copy-content=".fade.in {
  opacity: 1;
}"><pre class="notranslate"><code class="notranslate">.fade.in {
  opacity: 1;
}
</code></pre></div>
<p dir="auto">This resulted in a 100% solid black background. In order to get it working properly I added the following to my local site.css overrides:</p>
<div class="snippet-clipboard-content notranslate position-relative overflow-auto" data-snippet-clipboard-copy-content=".modal-backdrop.fade.in {
    opacity: .5;
}"><pre class="notranslate"><code class="notranslate">.modal-backdrop.fade.in {
    opacity: .5;
}
</code></pre></div>
<p dir="auto">Hi!</p>
<p dir="auto">I just generated a customized version and the modal background is totally black (I also generated a version without any change to be sure it wasn't me that caused that):</p>
<p dir="auto"><a target="_blank" rel="noopener noreferrer nofollow" href="https://camo.githubusercontent.com/7c884cd09470c8345f0304ad6c0a9768a9b9ad1b1cf415c28d5eb6df1beb82ab/68747470733a2f2f662e636c6f75642e6769746875622e636f6d2f6173736574732f353238373238352f313030393333382f66653335323434612d306233362d313165332d393531332d3962363637663362646665652e706e67"><img src="https://camo.githubusercontent.com/7c884cd09470c8345f0304ad6c0a9768a9b9ad1b1cf415c28d5eb6df1beb82ab/68747470733a2f2f662e636c6f75642e6769746875622e636f6d2f6173736574732f353238373238352f313030393333382f66653335323434612d306233362d313165332d393531332d3962363637663362646665652e706e67" alt="image" data-canonical-src="https://f.cloud.github.com/assets/5287285/1009338/fe35244a-0b36-11e3-9513-9b667f3bdfee.png" style="max-width: 100%;"></a></p>
<p dir="auto">The download link on the home page does have transparency:</p>
<p dir="auto"><a target="_blank" rel="noopener noreferrer nofollow" href="https://camo.githubusercontent.com/c35f738d5bc9c495c9e5c3e792a7c2a713e064f7ba536da495ecd6830f696e96/68747470733a2f2f662e636c6f75642e6769746875622e636f6d2f6173736574732f353238373238352f313030393335332f33396635313138342d306233372d313165332d383231622d3263396365363830626339352e706e67"><img src="https://camo.githubusercontent.com/c35f738d5bc9c495c9e5c3e792a7c2a713e064f7ba536da495ecd6830f696e96/68747470733a2f2f662e636c6f75642e6769746875622e636f6d2f6173736574732f353238373238352f313030393335332f33396635313138342d306233372d313165332d383231622d3263396365363830626339352e706e67" alt="image" data-canonical-src="https://f.cloud.github.com/assets/5287285/1009353/39f51184-0b37-11e3-821b-2c9ce680bc95.png" style="max-width: 100%;"></a></p>