Give the <article> a class, then style that class in main.css.
In main.css, give the .gallery {} selector a column-count:__ and the column-gap:__ properties. Then, in the .gallery figure {} rule, specify margin:0;
It is customary to assign the count to 1 for viewing on a phone, but with increasing counts depending on the width of the device. This example provides 2 for the skinnier window and 4 for a wider window. This change is handled using an @media query.
Stretch the browser window wider and skinnier to see how the figures sit side-by-side in sets of 2 or 4. This method has a flaw...do you see how the figcaption gets added to the second column?