You can change the size and the color of a Launcher in the general CSS.
Open the editor, go to "Customize", go to "CSS", go to the bottom of the CSS code.
Here's the code:
/* size of the XXX launcher */
.walkme-launcher-id-###### {
width: ##% !important;
height: ##px !important;
}
/* size of the XXX launcher */
Replace ###### with the ID of the launcher (found in editor, open the launcher, open notes).
Either choose the ## for percentage or amount of pixels.