How to upload a logo into the welcome box?

Hello Joelle ! 
– To upload a logo into the welcome box,  you can log in to  Dashboard > Pages > Home page, add the following code to the Heading 1 or Heading 2:

 <img src="FILE URL" />  

Notice: Please add the image to the Media, then copy the FILE URL on the right hand side and change the link here:  FILE URL
– If you want to change background for the welcome box, you can log in to Dashboard > Appearance > Customize > Style Selector.

See the screenshot: 

However, if you want to change background for each welcome box,you can add the following code to the Header Code:

 <style>
.block.head .block-inner {
    background: #....;
}
</style>

Hope this helps !