The current activity overview present two types of action buttons:

• outline secondary: for most elements
• subtle body: for completion element

This is expected. However, there are some problems with the applied style

• The outline border is darker than the subtle body.
• When hovering, both elements change the background to the secondary colour (dark grey by default), and the text turns to light. However, this is different from the prototype.
• When hovering, the dark grey background causes ugliness when the button has an alert badge.

It is important to note that the button styles must be standard and cannot be ad-hoc solutions only for the activity overview page. This means this issue may alter how one of the button styles is rendered on the entire platform. Making exceptions only for this page won't be acceptable.

From the technical perspective, the solution should:

1. Include all subtle buttons styles in \core\output\local\properties\button. From now on, this enum is the main provider for button classes and must include all core accepted styles.
2. Change the styling of some button (outline or subtle) to match the style. This is a UX decision.
3. Depending on the solution of the point 2, modify the styles of the alert badge (rendered using notice_badge method) so it changes the background and font color on hovering the button.