*{
    margin: 0;
    padding: 0;
}
.content{
    display: flex;
    text-align: center;
    margin-left: 0;
    
}
.content ul li{
    float: left;   
}
.leftbox{
    background-color: yellow;
    width: 25%; 
    padding-bottom: 5%; 
    text-decoration: none;
    overflow: hidden;   
}
.middlebox{
    background-color: lightblue;
    width: 25%; 
    padding-bottom: 5%;  
    text-decoration: none;
    overflow: hidden;
    
}
.rightbox{
    background-color: red;
    width: 25%; 
    padding-bottom: 5%; 
    text-decoration: none;
    overflow: hidden;
}
.poslední{
    background-color: orange;
    width: 25%; 
    padding-bottom: 5%;  
    text-decoration: none;
    overflow: hidden;
}
@media screen and (max-width: 900px){
 .content
 {
    display: block;
    
 }
 .leftbox
 {
    width: 100%;
 }
 .middlebox
 {
    width: 100%;
 }
 .rightbox
 {
    width: 100%;

 }
 .poslední
 {
    width: 100%;
 }