:root {
    --sidebar-size: clamp(300px, 20%, 400px);
}

@font-face {
    font-family: "Cantarell var";
    font-weight: 100 900;
    font-display: swap;
    font-style: normal;
    font-named-instance: "Regular";
    src: url("Cantarell-VF.otf") format("opentype");
}

h1 {
    margin: 20px;
}

* {
    margin: 0;
    padding: 0;
    font-family: Cantarell;
}

#links {
    display: inline-grid;
    grid-template-rows: 100% 0px;
}

#links > * {
    margin-left: 10px;
    margin-right: 10px;
}

#header {
    text-align: center;
    padding-top: 10%;
    padding-bottom: 10%;
    min-height: 40vh;
    background-image: url(https://www.state.gov/wp-content/uploads/2022/02/Kuwait-2323x1406.png);
    background-attachment: fixed;
}

.dropdown {
    background-color: aliceblue;
    padding: 10px;
    display: inline-block;
    grid-row: 1;
}

.dropdown-inner {
    background-color: white;
    display: flex;
    grid-row: 2;
    visibility: hidden;
    flex-direction: column;
}

.dropdown:hover + div > .dropdown-inner, .dropdown-inner:hover {
    visibility: visible;
}

.dropdown-inner > * {
    padding: 10px;
}

#content {
    margin: 10%;
}

#headin {
    padding-top: 2%;
    padding-bottom: 2%;
    transition: background-color 0.3s, color 0.3s;
}

#head-marker.scrolly-out + #headin {
    position: fixed;
    top: 0px;
    left: 0px;
    background-color: darkred;
    color: lightgreen;
    margin-left: var(--sidebar-size);
    width: calc(100vw - var(--sidebar-size));
}

#head-marker.scrolly-out + #headin > #links > * > *, #head-marker.scrolly-out + #headin > #links > * {
    background-color: black;
}

body {
    display: grid;
    grid-template-columns: var(--sidebar-size) auto;
}

#outer {
    position: relative;
    height: 100vh;
    overflow-y: scroll;
}

#sider {
    box-sizing: border-box;
    padding: 20px;
    background-color: pink;
}

.hidden {
    display: none;
}

#sider-cats {
    border-left: 2px solid white;
    padding-left: 10px;
}

#sider-cats > div {
    display: none;
    border-left: 2px solid red;
    padding-left: 10px;
}

#sider-cats > input:checked + label {
    border-right: 2px solid red;
    border-bottom: 2px solid red;
}

#sider-cats > label {
    color: green;
    padding-right: 10px;
    padding-bottom: 10px;
    display: inline-block;
}

#sider-cats > label:hover {
    color: darkgreen;
    cursor: pointer;
}

#sider-cats > input:checked + label + div {
    display: block;
}

#sider > h2 {
    border-right: 2px solid white;
    border-bottom: 2px solid white;
    text-align: center;
}

a {
    text-decoration: none;
    color: green;
}

a:hover {
    color: darkgreen;
}