As soon as I changed the HTML code ...and had added this...style="padding-bottom: 20px;" ..>
The layout of this section was horizontal and all three sections were like this:
but it changed to this.
I'm not seeing that you added style="padding-bottom:20px;" to the <div> with id=banner. Can you reapprove the landing page? Adding the style to the correct <div> should not have affected the section you have a screenshot of above.
The reason those 3 sections are stacking is because you have a typo where you are referencing the bootstrap.css file.
The file referenced here should be "bootstrap.css". You currently are referencing "bootstrap]". See the end of the href in the blue highlighted section.