Add remark to common.css, ycdl.css.

frontends/ycdl_flask/static/css/common.css

@@ -1,3 +1,8 @@
+/*
+This file contains styles that I want on almost all webpages that I make,
+not specific to one project.
+*/
+
 /*
 These properties are used by javascript functions.
 getComputedStyle(document.documentElement).getPropertyValue("--narrow").trim() === "1"

frontends/ycdl_flask/static/css/ycdl.css

@@ -1,3 +1,8 @@
+/*
+This file contains styles that apply to all pages within YCDL, but don't
+belong in common.css because they are specifically for this project.
+*/
+
 :root
 {
     --color_primary: white;