Confusion, possibly, that the highest level a user can apply in the Atto text editor is H3 (H1 and H2 being reserved for page header type content provided by core/theme renderers).
You can, though, change the *style* applied to any element, including H1 and H2, by appropriately targeting CSS (or SCSS in some themes) selectors.
You can, though, change the *style* applied to any element, including H1 and H2, by appropriately targeting CSS (or SCSS in some themes) selectors.