html * { /* descendent selector */
    box-sizing: border-box;
}

:root { /* to store CSS variables, outside the rendered document */
    --primary-color: #000000;
    --secondary-color: #eeddaa;
    --tertiary-color: #6a5acd;
}

body {
    font-family: system-ui, sans-serif;
    font-size: 100%;
    line-height: 135%;
    background-color: var(--primary-color);
    color: var(--secondary-color);
    margin: 2em;
    background-image: linear-gradient(#0008, #0008),url(rainforest.jpg);
    background-position: center;
}

header {
    min-height: 30vh;
    background-color: var(--tertiary-color);
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
}

h1 {
    line-height: 1.2em;
    text-align: center;
}

h2 {
    text-align: center;
}

a {
    color: var(--secondary-color);
}

.flex-parent {
    display: flex;
    flex-direction: column;
}

.flex-item {
    display: flex;
}

img {
    border: 1px solid var(--primary-color);
    border-radius: 10px;
    padding: 10px;
    background-color: var(--secondary-color);
    max-width: 100%;
    height: auto;
}

.grid {
    display: grid;
    grid-template-columns: 1fr 1fr;
    grid-template-rows: 200px 200px 200px;
    grid-auto-flow: dense;
    gap: 1em 3em;
}

.palette1 {
    background-color: red;
}

.palette2 {
    background-color: yellow;
}

.palette3 {
    background-color: blue;
}

.palette4 {
    background-color: orange;
}

.palette5 {
    background-color: green;
}

.palette6 {
    background-color: purple;
}

@media(min-width: 550px) {

    .flex-parent {
        display: flex;
        flex-direction: row;
        justify-content: space-evenly;
    }

    .flex-item {
        display: flex;
        flex: 50%;
    }

    .grid {
        display: grid;
        grid-template-columns: 1fr 1fr 1fr;
        grid-template-rows: 200px 200px;
        grid-auto-flow: dense;
        gap: 1em 3em;
    }
}