body {
    margin: 0;
    padding: 0;
    font-family: Arial, sans-serif;
}
header {
    width:100%;
    background-color: darkgray;
    color: white;
    font-size: 300%;
    text-align: center;
}
#kolumna1 {
    width: 45%;
    float: left;
    padding: 20px;
}
#kolumna2 {
    width: 45%;
    float: left;
    padding: 20px;
}
main {
    width: 80%;
    float: left;
    padding: 20px;
}
menu {
    width: 200px;
    float:left;
    padding: 0;
    margin: 0;
    background-color: #ccc;
    height: 100vh;
}
menu ul {
    margin: 0%;
    padding: 0%;
}
menu ul li {
    margin: 0%;
    list-style-type:none;
    padding: 0%;
}
menu ul li a {
    margin: 0%;
    text-decoration: none;
    display: block;
    color: black;
    font-weight: bold;
    border-bottom: 1px solid gray;
    padding: 5px  15px;
    padding: 0%;
}
menu ul li a:hover {
    background-color: red;
    color: white;
    transition: 0,3s;
}
footer {
    clear: both;
    text-align: center;
}