add gif demo

docs/assets/css/style.css

@@ -135,3 +135,29 @@ img {
     position: relative;
     height: 30%;
 }
+
+.popups {
+    display: none;
+    justify-content: center;
+    align-items: center;
+    position: fixed;
+    z-index: 999;
+    left: 0;
+    top: 0;
+    right: 0;
+    bottom: 0;
+    width: 100%;
+    height: 100%;
+    background: rgba(0, 0, 0, 0.5);
+}
+
+.popups .popinner {
+    display: flex;
+    justify-content: center;
+    align-items: center;
+    width: 800px;
+    height: 600px;
+    background: #2b2b2b;
+    border-radius: 3px;
+    padding: 20px;
+}