.main_container {
    left: 0px;
    width: 99%;
    top: 0px;
    height: 98%;
    border:5px solid green;
}  
.header {
    left: 0px;
    top: 0px;
    width: 100%;
    height:15%;
    border:2px solid black; 
}
.menu {
    float:left;
    left:0px;
    top:17%;
    width: 15%;
    height:84%;
    border:2px solid black;
}
.second_menu {
    display:none;
    float:left;
    border:2px dashed blue;
    width:10%;
    height:84%;
    float:left;
    margin-right:5px;
    left:16%;
    top:17%;
}
.mbtn {
    border-radius:35%;
    border-color:yellow;
    width:150px;
    height:50px;
    font-size:20px;
    color:yellow;
    background-color:black;
}