header{
    background-image: linear-gradient(
rgba(100,100,100,1)	,
rgba(120, 120, 120, 1))	, url("");
padding: 15px;
text-align: center;
font-size: 20px;
top:0;
position: sticky;
}
header a{
color:aqua;
margin: 0 40px;
padding: 10px;
border-radius: 30px;
text-decoration: none;
font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
}

header a.BoutonBleu:hover{
color:rgb(48, 48, 48);
background-color: aqua;
}