fix: reduce footnote size, fix red plaintext code

assets/css/style.scss

@@ -25,3 +25,17 @@ div.highlight {
 .MathJax {
     font-size: 90%;
 }
+
+div.year.lead {
+    font-family: "Source Sans Pro", "Microsoft Yahei", sans-serif;
+}
+
+div.language-plaintext.highlighter-rouge {
+    pre {
+        color: #3f596f;
+    }
+}
+
+div.footnotes {
+    font-size: 80%;
+}