.header{position:fixed!important}  
      @media  screen and ( min-width:1680px){
.main_colum {
    float: left;
    width: 100%;
    min-height: calc(100vh - 160px);
    background-color: #f8f9fa;
  padding-top:90px;
}
}

@media screen and (max-width:1679px ) and ( min-width:1440px){
.main_colum {
    float: left;
    width: 100%;
    min-height: calc(100vh - 150px);
    background-color: #f8f9fa;
    padding-top:80px;
}
}

@media screen and (max-width:1440px ) and ( min-width:1280px){
.main_colum {
    float: left;
    width: 100%;
    min-height: calc(100vh - 134px);
    background-color: #f8f9fa;
  padding-top:70px;
}
}

@media screen and (max-width:1280px ) and ( min-width:960px){
.main_colum {
    float: left;
    width: 100%;
    min-height: calc(100vh - 117px);
    background-color: #f8f9fa;
   padding-top:60px;
}
}
@media screen and (max-width:959px ) and ( min-width:640px){
.main_colum {
    float: left;
    width: 100%;
    min-height: calc(100vh - 110px);
    background-color: #f8f9fa;
   padding-top:60px;
}	
}
@media only screen and (max-width:639px){
.main_colum {
    float: left;
    width: 100%;
    min-height: calc(100vh - 115px);
    background-color: #f8f9fa;
    padding-top:0.42rem;
}
}