Horizontal alignment is selected with an icon choice for left, center, or right. For text, the horizontal alignment setting is usually in the Typography > Font section on the Style tab. For other elements, such as a Photo module, the setting appears in the Align field on the Style tab.
These alignment options are toggles, which can be turned on and off. If no option is selected, alignment is the default setting, such as one set by the theme.
In most cases, the new alignment UI also has a responsive icon, as shown in this screenshot, so you can set alignment according to device size.