Update screenshots and theme tags

assets/book.scss

@@ -140,14 +140,21 @@ ul.pagination {
 .book-search {
   position: relative;
   margin: $padding-16 0;
+  border-bottom: 1px solid transparent;
+
+  &::after {
+    display: block;
+    content: "";
+    clear: both;
+  }
 
   input {
+    width: 100%;
+    padding: $padding-8;
+
     border: 0;
     border-radius: $padding-4;
 
-    padding: $padding-8;
-    width: 100%;
-
     background: $gray-100;
 
     &:required + .book-search-spinner {
@@ -170,10 +177,6 @@ ul.pagination {
 
     @include spin(1s);
   }
-
-  li:last-child {
-    margin-bottom: $padding-16 * 2;
-  }
 }
 
 .book-toc {