body {
    background-color: rgb(25, 25, 25);
    height: 100vh;
    overflow: hidden;
}

header {
    position: absolute;
    top: 10px;
    right: 10px;
    left: 80px;
    height: 50px;
    width: calc(100% - 90px);
    background-color: black;
    border-radius: 10px;
    color: white;
    display: flex;
    align-items: center;
    padding: 5px;
}
header:hover {
    border: solid 2px #00c3ff;
}

nav {
    position: absolute;
    top: 10px;
    left: 10px;
    bottom: 10px;
    width: 60px;
    height: calc(100% - 20px);
    background-color: black;
    border-radius: 10px;
    color: white;
    display: block;
}
nav:hover {
    border: solid 2px #00c3ff;
}

.boxes {
    position: relative;
    height: calc(100% - 70px);
    width: calc(100% - 90px);
    background-color: red;
}