The secondary logo dimension can be manipulated by it's background-size CSS property value. This article describes how a secondary logo can be displayed through the site editor, while the background-size CSS property value can be set on the same left sidebar once the secondary logo is enabled, as shown below.
Different options can be used to fit the logo to your preferred design, such as auto, contain and cover. Numerical values can also be used including their unit of expressions, such as percentage and pixel.
More information can be found upon hovering over the tooltip (question mark icon next to the background-size field) which can also be found in this resource site.
To set values for the secondary logo background-size property:
1. Display the secondary logo through the site editor. You can refer to this site for more details.
3. Indicate your preferred setting for the background-size. In the illustration above, the value is set to 101%.
4. Click on Done Editing.