Float problems

We don't use floats much anymore.  It's not wrong to use floats but it's not modern.  With Flexbox you have more control over how things line up.

https://www.w3schools.com/css/css3_flexbox.asp

Try adding a . in front of the container class on line 8.

Class selectors start with a .
    Example: .container {}
ID selectors start with a #
    Example: #navigation {}
HTML element selectors are written without either
    Example: img {}

DW is/was not great at showing the actual layout correctly in Design View, although it may have improved in recent years, since I last used it.

Do the images show up horizontally when you view in the browser? I can't see anything wrong with your code.