Move progress css style to dedicated file

In kthoom implementation, there is also a DOM

    `<div id="progress"....>`

If this part of css style stays in main.css, it also effects the kthoom
implementation, therefore the progress bar will disappear when reading
comic files (such as cbz).

cps/static/css/main.css

@@ -918,10 +918,3 @@ input:-moz-placeholder {
 .icon-resize-small::before {
   content: "\e808";
 } /* '' */
-
-#progress {
-  right: 4rem;
-  bottom: 2px;
-  width: fit-content;
-  position: absolute;
-}

cps/static/css/reader.css

@@ -72,3 +72,10 @@
   right: 50px;
   // position: absolute;
 }
+
+#progress {
+  right: 4rem;
+  bottom: 2px;
+  width: fit-content;
+  position: absolute;
+}