Improved the responsiveness of img.

Without this tweak, when the viewport is smaller than the image, the image overflows the page.
With this commit it will be resized to fit the available width.

static/css/main.css

@@ -88,3 +88,7 @@ a:hover {
 footer {
     border-bottom: var(--border-width) solid var(--accent);
 }
+
+img {
+    max-width: 100%;
+}