So, I’m trying to change a part of my website, and i can’t get it to work. The css part of the code is this:

/*new timeline*/
:root {
    scroll-behavior: smooth;
}

* {
    margin: 10% 0;
    padding: 1% 0;
    box-sizing: content-box;
    width: 50%;
}

body {
    display: block;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    background-color: rgb(170, 230, 189);
}

header {
    display: flex;
    flex-direction: column;
    align-items: center;
    row-gap: 5%;
    margin-top: 5%;
}

header h1 {
    background-color: #fff;
    padding: 1% 0;
    border-radius: 50% 20% / 10% 40%;
    color: green;
    font-size: 1.5rem;
}

header p {
    font-size: 1.25rem;
}

.main-container {
    margin-top: 5%;
    margin-bottom: 5%;
    margin-left: 5%;
    margin-right: 5%;
    width: 100%;
    display: inline-block;
    flex-direction: column;
    align-items: center;
}

.line {
    position: relative;
    left: 50%;
    height:100%;
    width: 80%;
    display: flex;
    align-items: center;
    justify-content: center;
    border-radius: 10%;
    transform: translateX(-5%);
    background-color: blue;
}

.line a {
    text-decoration: none;
    display: flex;
    align-items: center;
    justify-content: center;
    position: relative;
    bottom: 0;
    width: 80%;
    height: 80%;
    font-weight: bold;
    color: rgb(55, 131, 65);
    background-color: #fff;
    border-radius: 50%;
    cursor: pointer;
    overflow: auto;
}

.card {
    font-size: .8rem;
    width: 200px;
    height: 150px;
    border-radius: 10px;
    background-color: white;
    margin-bottom: 10px;
}

.left {
    position: relative;
    left: -10%;
    right: 10%;
}

.right {
    position: relative;
    left: 10%;
}

.left::after,
.right::after {
    content: '';
    position: relative;
    width: 80%;
    height: 80%;
    background-color: rgb(18, 113, 48);
    border-radius: 0px 10px;
    transform: rotate(-45deg);
    z-index: -1;
}

.left::after {
    top: 80%;
    right: -80%;
}

.right::after {
    top: 80%;
    left: -80%;
}

.card h1 {
    padding: 80%;
    display: flex;
    justify-content: center;
    border-radius: 0 0 0 0;
    color: white;
    background-color: rgb(18, 113, 48);
}

.card p {
    padding: 80%;
}

.thumbnail {
    position: relative;
    top: 0;
    width: 80%;
    height: 80%;
    border-radius: 80%;
    overflow: hidden;
}

.thumbnail img {
    width: 100%;
    height: 100%;
}

.left .thumbnail {
    left: 80%;
}

.right .thumbnail {
    right: 80%;
}

@media screen and (max-width:790px) {
    body {
        text-align: center;
        padding: 0 10%x;
    }

    .main-container {
        width: auto;
    }

    .line {
        height: 80%;
    }

    .card {
        top: 80%;
        margin-bottom: 80%;
    }

    .left::after,
    .right::after {
        visibility: hidden;
    }

    .left {
        left: auto;
    }

    .right {
        left: auto;
    }

    .left .thumbnail {
        top: -80%;
        left: 80%;
    }

    .right .thumbnail {
        top: -80%;
        left: 80%;
    }
}

What I’m aiming at, is to get the content of the page always centered, and at the same time adapting to browser size, page size, or device type. I have other pages on my site, and they all work fine, so it has to be something with this part of the code.

Is there something I have to change or to add, in order to get this to work as I want it to?