When using the WordPress Gallery Option, the image size of gallery pics is set automatically when the theme is activated, all you have to do then is to insert the gallery shortcode with a max of 7 columns.
NOTE: If the code snippets produce a different result on your site, it may be because the settings on your site are different or due to any customization already added to achieve a similar result. Please try removing your customization if any and feel free to change the values in the example codes to suit your design.
By default, the gallery thumbnail is displayed at the bottom of the big image. In this example let’s take a look at gallery thumbnail alignment. How we can move it to the right side of the big image. Start by adding a custom CSS class name “av-gallery-style-1” to the gallery element.