style: update popup width and document styles

- Change popup width from 800px to 71rem for better scaling
- Add DM Sans as default body font
- Set h1 font-size to 3rem
- Reduce paragraph bottom margin from 10mm to 5mm
- Add link styles (purple color, no underline)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

public/assets/css/stylesheet.css

@@ -10,6 +10,14 @@
   }
 }
 
+body {
+  font-family: "DM Sans", sans-serif;
+}
+
+h1 {
+  font-size: 3rem;
+}
+
 h2 {
   break-before: page;
 }
@@ -24,13 +32,18 @@ h2 {
 
 p {
   font-size: 1rem;
-  margin: 0mm 0mm 10mm 0mm;
+  margin: 0mm 0mm 5mm 0mm;
+}
+
+li p {
+  margin-bottom: 0;
 }
 
 img {
   width: 100%;
 }
 
-li p {
-  margin-bottom: 0;
+a {
+  color: #7136ff;
+  text-decoration: none;
 }