.plenka{
    display: flex;
    justify-content: center;
    width:100%;
    flex-flow:row wrap;
    align-items:flex-start;
}
.plenka img{
    width:33.33%;
}

.plenka_primer,
.plenka_top{
    display: flex;
    justify-content: center;
    width:100%;
    flex-flow:row wrap;
}
.plenka_primer img{
    padding:10px 20px 10px 20px;
    width:25%;
}

@media screen and (max-width:767px){
    .plenka img{
        width:100%;
        padding:10px 20px;
    }
    .plenka_primer img{
        width:50%;
    }
}