Blog page with posts from specific categories

Please add following code

$args = array(
    'post_type' => 'post',
    'post_status' => 'publish',
    'category__and'   => array( 2, 6 ),
    'posts_per_page' => 1,
);
$arr_posts = new WP_Query( $args );

OR

$tax_query = array(
relation => 'AND',
array(
    'taxonomy'          => 'category',
    'field'             => 'term_id',   // 'term_id' by default, so just here as an example
    'terms'             => 186,
    'include_children'  => false,       // true by defualt
    'operator'          => 'IN'         // 'IN' by default, so just here as an example
),
array(
    'taxonomy'          => 'category',
    'terms'             => 187,
    'include_children'  => false,       // true by defualt
)

)