Replace solid background image with semi-transparent overlay

The change adds a dark semi-transparent gradient overlay to the background
image to improve text readability. This creates better contrast between
the foreground content and background image while maintaining visibility
of the underlying image.

static/index.html

@@ -27,7 +27,7 @@
             left: 0;
             width: 100%;
             height: 100%;
-            background-image: url('_.jpeg');
+            background-image: linear-gradient(rgba(0, 0, 0, 0.5), rgba(0, 0, 0, 0.5)), url('_.jpeg');
             background-size: cover;
             background-position: center;
             background-repeat: no-repeat;