Update basic.mdx

Update Some Important Selectors Tags that are used in CSS.

content/batch/learn/css/basic.mdx

@@ -121,6 +121,38 @@ h1 {
   color: green;
 }
 
+Add More important Selectors tags that really used.
+Essential Selectors Tag that Really used.
+
+/* Child Selector (using > ) */
+div>p {
+background-color: green;
+}
+
+/* Descendant Selector */
+
+.div p {
+background-color: maroon;
+}
+
+/* Universal Selector (ALL Elements margin and padding are 0; ) */
+
+{
+margin: 0;
+padding: 0;
+}
+/* Pseudo Selector */
+
+/* If you visited the website then you can change the color */
+a:visited {
+color: red;
+}
+
+/* If you want to change link color before visit */
+a:link {
+color: blueviolet;
+}
+
 /* Specificity example */
 .heading#title {
   color: yellow;