header.css

/* --- HEADER --- */
/* 1 */
header {
    height: 100vh; /* 2 */
    background-color: #1A5275;
}

/* NAV */
/* 3 */
.main-nav {
    display: block;
    float: right;
    list-style: none;
    margin-top: 50px;
}

.main-nav li {
    display: inline-block;
    margin-left: 40px;
}

/* 4 */
.main-nav li span {
    padding: 8px 0;
    color: #1A5275;
    font-size: 90%;
    border-bottom: 2px solid transparent; /* 5 */
    -webkit-transition: border-bottom 0.2; /* 5 */
    transition: border-bottom 0.2; /* 5 */
}

/* 6 */
.main-nav li span:hover {
    cursor: pointer;
    border-bottom: 2px solid #ffb510;
}

/* NAV GRUDENTA */
/* 7 */
.grudenta {
    z-index: 1000;
    position: fixed; 
    top: 0; 
    left: 0;
    width: 100%;
    background-color: #ffffff;
    font-size: 80%;
    margin: auto 0;
}

/* 8 */
.grudenta ul {
    margin-top: 25px;
    font-size: 135%;   
}