Add viewport meta tag.

custom-viewport.php

<?php
//* Do NOT include the opening php tag shown above. Copy the code shown below.

//* Add custom Viewport meta tag for mobile browsers
add_action( 'genesis_meta', 'sp_viewport_meta_tag' );
function sp_viewport_meta_tag() {
	echo '<meta name="viewport" content="width=device-width, initial-scale=1.0"/>';
}

viewport.php

<?php
//* Do NOT include the opening php tag shown above. Copy the code shown below.

//* Add Viewport meta tag for mobile browsers (requires HTML5 theme support)
add_theme_support( 'genesis-responsive-viewport' );