The Show More Button tab will be visible if you select the Tiles or Hierarchy Grid layout. You will find the following options there. 

1) Button Label: You can edit the button label as you wish for the Gird and Hierarchy Grid layout. 

2) Font Size: Set the Show More button font size as per your need from here. 

3) Color: Set the Show More button Color, Hover Color, Background, and Hover Background color as you wish.

4) Border: Set the border width, style, color, and border-radius as per your need from here.

5) Box Shadow: Select any of the box shadow options you want from here. 

6) Padding: Set paddings for the Show More button as you want in different units like (px, %, em).

7) Margin: Set the margin values as you want for the Show More button.