html - Responsive CSS issues on different iOS devices -

i have couple of issues css, using w3.css library build basic responsive website, have media queries small devices , reason works on phone not on computer when resize small size, used work on old version of site not anymore.

the second issue recent, in fact it's today; reason website not work on different 'iphone'.. explanation because different ios version? 'iphone' ios10.3 , phone on ios10.1.1

in conclusion, add, should change library bootstrap or w3.css enough? sorry if come out bit naive new responsive design.

homepage code example:

.main-div{   //main div supposed main content box   max-width: 75%;   width: 100%; } .sidebar-div{ //sidebar div supposed sidebar content box   max-width: 24%;   width: 100%; }  /* responsive css */    /* mobile portrait&landscape */    @media screen and(max-width: 768px){     .main-div, .sidebar-div{       max-width: 100%;     }   }