It would be great if you want to add a button compatibility for my mod.

To make this mod compatible with your sapphire skin 3 steps are needed :

Step 1

Make at least one icon for the button and place it inside the Sprites folder of your skin (my default button have 4 states -> Normal,Hovered,Pressed and Focused)

Step 2

Add your code in your ModCompatibility.xml after last mod

Example :

<!-- Favorite Cims -->
<Component name="TSBar">
<Component name="MainToolstrip">
<Component name="FavCimsButton" optional="true">
<normalBgSprite>FavoriteCimsButton</normalBgSprite>
<hoveredBgSprite>FavoriteCimsButtonHovered</hoveredBgSprite>
<pressedBgSprite>FavoriteCimsButtonPressed</pressedBgSprite>
<focusedBgSprite>FavoriteCimsButtonFocused</focusedBgSprite>
<disabledBgSprite>FavoriteCimsButtonDisabled</disabledBgSprite>

<tooltip>Favorite Cims</tooltip>
<atlas>IconsAtlas</atlas>
<size>48.0, 48.0</size> <!-- your own button dimension -->

<!-- position, if different then normal -->

</Component>
</Component>
</Component>

Step 3

Inside skin.xml, after <SpriteAtlas name="IconsAtlas"> :

<Sprite name="FavoriteCimsButton">Sprites/YourOwnButtonOfMyModVersionNormal.png</Sprite>
<Sprite name="FavoriteCimsButtonHovered">Sprites/YourOwnButtonOfMyModVersionHovered.png</Sprite>
<Sprite name="FavoriteCimsButtonPressed">Sprites/YourOwnButtonOfMyModVersionPressed.png</Sprite>
<Sprite name="FavoriteCimsButtonFocused">Sprites/YourOwnButtonOfMyModVersionFocused.png</Sprite>
<Sprite name="FavoriteCimsButtonDisabled">Sprites/YourOwnButtonOfMyModVersionNormal.png</Sprite>