You should take no notice of how the site display in DW's design view because it is not a browser. It handles css very badly and should not be used in wysiwyg view at all.
Just use code view and then preview in a real browser to see what it looks like.
If you change code to make it display better in design view then that's like the tail wagging the dog
Having said all that you can probably make it look better by floating this.
However adding code where none is necessary is a big hack.