added CSS for popup

dist/css/style.css

@@ -0,0 +1,40 @@
+h1 {
+  margin: 0;
+  padding: 0;
+}
+html, body, .app {
+  margin: 0;
+  padding: 0;
+  position: relative;
+  width: 100%;
+  height: 100vh;
+}
+.popup {
+  position: fixed;
+  width: 100%;
+  height: 100%;
+  top: 0;
+  left: 0;
+  right: 0;
+  bottom: 0;
+  margin: auto;
+  background-color: rgba(0,0,0, 0.5);
+}
+.popup_inner {
+  position: absolute;
+  left: 25%;
+  right: 25%;
+  top: 25%;
+  bottom: 25%;
+  margin: auto;
+  background: white;
+}
+
+.footer {
+  position: absolute;
+  bottom: 0;
+  width: 100%;
+  /* Set the fixed height of the footer here */
+  height: 60px;
+  background-color: #f5f5f5;
+}