fixing sacing strings example

Author: rachelandrew

learn/values-units/strings-idents.html

@@ -33,15 +33,15 @@
 
     <textarea class="playable playable-css" style="height: 240px;">
 .box {
-    width:400px;
-    padding: 1em;
-    border-radius: .5em;
-    border: 5px solid rebeccapurple;
-    background-color: lightblue;
+  width:400px;
+  padding: 1em;
+  border-radius: .5em;
+  border: 5px solid rebeccapurple;
+  background-color: lightblue;
 }
 
 .box::after {
-    content: "This is a string. I know because it is quoted in the CSS."
+  content: "This is a string. I know because it is quoted in the CSS."
 }
     </textarea>