Fix code according to the comment

Update code, change file name.

practice/practice-02/src/styles/components/_button.scss

@@ -1,6 +1,5 @@
 .btn {
   align-self: center;
-  display: none;
   padding: 13px 20px;
   background-color: $primary-color;
   border-radius: 100px;
@@ -11,8 +10,12 @@
   transition: 0.2s;
 }
 
+.nav-download-btn {
+  display: none;
+}
+
 @media screen and (min-width: 840px) {
-  .btn {
+  .nav-download-btn {
     display: block;
 
     &:hover {