Drupal change the number of items in view PHP
insert HTML markup on the View header and make three buttons with HTML markup and then link each of the button like

&lt;ul&gt;
  &lt;li&gt;&lt;a href="/search?items_per_page=10"&gt;10 elements&lt;/a&gt;&lt;/li&gt;
  &lt;li&gt;&lt;a href="/search?items_per_page=20"&gt;20 elements&lt;/a&gt;&lt;/li&gt;
  &lt;li&gt;&lt;a href="/search?items_per_page=30"&gt;30 elements&lt;/a&gt;&lt;/li&gt;
&lt;/ul&gt;


After this you can style the button however you want.