CSS Float使内容缩小到较小的屏幕

While using media queries for screen resolutions of tablet and mobile phones, the "sideNav" which contains all the links and the social media buttons on the right hand side does remain floated but the "maincontent" section containing all the content goes down and does not stay up floating the "sideNav". I am not able to understand why? The "sideNav" normally floats on the right of the "maincontent" but it does not on resizing.While using media queries for screen resolution