index.css

:root {
    --primary: #000000;
    --txt: #ffffff;
}

* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
    font-family: Verdana, Geneva, Tahoma, sans-serif;
}

body {
    overflow-x: hidden;
    background-image: linear-gradient(to top, #f3a90a, #f88989, #64939b, #203e4d, #250125, #000000);
    min-height: 10vh;
}

.barre-menu {
    position: fixed;
    top: 4;
    left: 0;
    width: 100%;
    font-size: 18px;
    padding: 10px 100px;
    display: blocks;
    justify-content: space-around;
    align-items: center;
    z-index: 10;
}

.dropdownmenu {
    position: fixed;
    right: 20px;
    top: 40px;
    border-radius: 40px;
}


/* ----------------MENU-------1-------------------------------------------

        #header ul {
            display: flex;
            justify-content: center;
            align-items: flex-start;
        }
        
        #header ul li {
            list-style: none;
            margin-left: 40px;
        }

        #header ul li a {
            text-decoration: none;
            padding: 10px 15px;
            color: var(--txt);
            border-radius: 20px;
        }
        
        #header ul li a:hover,
        #header ul li a.active {
            background: var(--primary);
        }
        
        ----------------MENU---1-----------------------------------------------*/


/*------------MENU----2--------------------------------------------------------*/

.dropdownmenu ul,
.dropdownmenu li {
    margin: 0;
    padding: 0;
}

.dropdownmenu ul {
    background: var(--primary);
    list-style: none;
    width: 100%;
}

.dropdownmenu li {
    float: right;
    position: relative;
    width: auto;
}

.dropdownmenu a {
    background: transparent;
    color: #FFFFFF;
    display: block;
    padding: 10px 25px;
    text-align: center;
    text-decoration: none;
    border-radius: 10%;
    -webkit-transition: all .25s ease;
    -moz-transition: all .25s ease;
    -ms-transition: all .25s ease;
    -o-transition: all .25s ease;
    transition: all .25s ease;
}

.dropdownmenu li:hover a {
    background: #000000;
    border-radius: 10%;
}

#submenu {
    left: 0;
    opacity: 0;
    position: absolute;
    top: 35px;
    visibility: hidden;
    text-align: center;
    z-index: 1;
}

li:hover ul#submenu {
    opacity: 1;
    top: 40px;
    /* adjust this as per top nav padding top & bottom comes */
    visibility: visible;
    background-color: transparent;
}

#submenu li {
    float: none;
    width: 100%;
}

#submenu a:hover {
    background-color: #ffffff96;
}

#submenu a {
    background-color: transparent;
}


/*------------------------MENU---2-----------------------------------------------------------*/

#btn {
    text-decoration: none;
    display: inline;
    padding: 8px 30px;
    background: rgba(255, 255, 255, 0.46);
    color: var(--txt);
    font-size: 1.2em;
    font-weight: 500;
    letter-spacing: 2px;
    border-radius: 40px;
    transform: translatey(100px);
    z-index: 3;
}

#btn:hover {
    background: rgba(255, 255, 255, 0.964);
    color: black;
}

.star {
    position: absolute;
    width: 1px;
    height: 1px;
    border-radius: 50%;
    animation-iteration-count: infinite;
}

.shooting {
    z-index: 100;
    position: relative;
    top: 30%;
    left: 30%;
    width: 500px;
    height: 5px;
    border-radius: 5px;
    display: inline-block;
    transform: rotateZ(-45deg);
}

.shooting .core {
    display: inline-block;
    position: absolute;
    top: 0;
    left: 0;
    width: 4px;
    height: 4px;
    border-radius: 50%;
    background: #f7f7f1;
    box-shadow: 0px 0px 3px 1px #ffffff, 0px 0px 10px 5px #fffffff1;
    animation: 6s linear infinite core;
}

.shooting .trail {
    display: inline-block;
    position: absolute;
    content: '';
    width: 100px;
    height: 5px;
    border-radius: 50% 0 0 50%;
    background: linear-gradient( to right, #f7c9aedc, #f3f3b1d5 50%, transparent);
    top: -1px;
    left: 0;
    animation: 6s linear infinite trail;
}

@keyframes core {
    0% {
        left: 100%;
        opacity: 1;
    }
    15% {
        left: 30%;
        opacity: 0.8;
    }
    30% {
        left: 0;
        opacity: 0;
    }
    100% {
        left: 0;
        opacity: 0;
    }
}

@keyframes trail {
    0% {
        left: 100%;
        opacity: 1;
        width: 0;
    }
    15% {
        left: 35%;
        opacity: 0.5;
        width: 150px;
    }
    30% {
        left: 10%;
        opacity: 0;
        width: 150px;
    }
    100% {
        left: 0;
        opacity: 0;
        width: 150px;
    }
}

section {
    position: relative;
    width: 100%;
    height: 100vh;
    display: flex;
    justify-content: center;
    align-items: center;
}

section::before {
    content: "";
    position: absolute;
    bottom: 0;
    left: 0;
    width: 100%;
    height: 100px;
    /*z-index: 10;*/
}

section img {
    position: absolute;
    top: 0px;
    left: 0;
    width: 100%;
    height: 100%;
    object-fit: cover;
    pointer-events: none;
}

section #text {
    position: absolute;
    color: var(--txt);
    font-size: 10vw;
    text-align: center;
    line-height: .55em;
    font-family: Arial, Helvetica, sans-serif;
    opacity: 33%;
}

section #text span {
    font-size: .20em;
    letter-spacing: 2px;
    font-weight: 400;
}

.sec {
    position: relative;
    padding: 100px;
    background: var(--primary);
    z-index: 15;
}

.sec h2 {
    font-size: 3.5em;
    color: #fff;
    margin-bottom: 8px;
}

.sec p {
    font-size: 1em;
    color: #fff;
}

footer {
    position: fixed;
    padding: 20px 100px;
    background: var(--primary);
}

footer a {
    text-decoration: #f88989;
    color: #fff;
}

#cosmos {
    opacity: 20%;
    position: fixed;
    margin-top: -10%;
}

#stars {
    rotate: 55°;
    opacity: 100%;
}

#forest {
    z-index: 5;
}

footer {
    color: var(--txt);
    text-align: center;
    margin-bottom: 0px;
    position: relative;
    z-index: 10;
}


/*
        .iss {
            z-index: 100;
            position: relative;
            animation: mymove 20s infinite;
        }
        
        @keyframes mymove {
            from {
                right: 0px;
            }
            to {
                right: 1400px;
            }
        }*/

h4 {
    color: var(--txt);
    font-size: 18px;
}

#scale,
a {
    color: #f3a90a;
    text-decoration: none;
}

#secret {
    background-color: transparent;
    color: #000000;
    font-size: 10px;
    position: relative;
    margin-right: 20px;
    z-index: 100;
}

#secret:hover {
    background-color: #ffffff96;
    border-radius: 40px;
}

a:hover {
    opacity: 50%;
}

#projet {
    display: flex;
    flex-direction: row;
    width: auto;
    height: auto;
}