Update user_config/docs/theme/css/extra.css

Add Popup and link css style

user_config/docs/theme/css/extra.css

 .image-center {
   display : block;
   margin  : auto;
-}
+}
\ No newline at end of file
+
+.Popup {
+  position: relative;
+  display: none;
+  opacity:0;
+  -webkit-transition: opacity 400ms ease-in;
+  -moz-transition: opacity 400ms ease-in;
+  transition: opacity 400ms ease-in;
+}
+
+.Popup:target {
+  display: inline;
+  opacity:1;
+}
+
+.Popup > div {
+  position: relative;
+  padding: 5px 20px 13px 20px;
+  border-radius: 10px;
+  background: #364653;
+}
+
+.close {
+  background: #606061;
+  color: #FFFFFF;
+  line-height: 25px;
+  position: absolute;
+  right: -12px;
+  text-align: center;
+  top: -10px;
+  width: 24px;
+  text-decoration: none;
+  -webkit-border-radius: 12px;
+  -moz-box-shadow: 1px 1px 3px #000;
+}
+
+.close:hover { background: #00d9ff; }
+
+.md-typeset a {
+  color: rgba(var(--md_color__blue_500),1.00);
+}