* {
border: 0;
box-sizing: border-box;
margin: 0;
padding: 0;
}
:root {
--hue: 223;
--bg: hsl(var(--hue),10%,90%);
--fg: hsl(var(--hue),10%,10%);
--primary: hsl(var(--hue),90%,50%);
--trans-dur: 0.3s;
--trans-timing: cubic-bezier(0.65,0,0.35,1);
font-size: calc(16px + (24 - 16) * (100vw - 320px) / (2560 - 320));
}
a {
color: var(--primary);
transition: color var(--trans-dur);
}
body,
button {
color: var(--fg);
font: 1em/1.5 "IBM Plex Sans", sans-serif;
}
h1 {
font-size: 2em;
margin: 0 0 3rem;
padding-top: 1.5rem;
text-align: center;
}
.btn {
background-color: var(--fg);
border-radius: 0.25em;
color: var(--bg);
cursor: pointer;
padding: 0.375em 0.75em;
transition:
    background-color calc(var(--trans-dur) / 2) linear,
    color var(--trans-dur);
-webkit-tap-highlight-color: transparent;
}
.btn:hover {
background-color: hsl(var(--hue),10%,50%);
}
.btn-group {
display: flex;
gap: 0.375em;
margin-bottom: 1.5em;
}
.timeline {
margin: auto;
padding: 0 1.5em;
width: 100%;
max-width: 36em;
}
.timeline__arrow {
background-color: transparent;
border-radius: 0.25em;
cursor: pointer;
flex-shrink: 0;
margin-inline-end: 0.25em;
outline: transparent;
width: 2em;
height: 2em;
transition:
    background-color calc(var(--trans-dur) / 2) linear,
    color var(--trans-dur);
-webkit-appearance: none;
appearance: none;
-webkit-tap-highlight-color: transparent;
}
.timeline__arrow:focus-visible,
.timeline__arrow:hover {
background-color: hsl(var(--hue),10%,50%,0.4);
}
.timeline__arrow-icon {
display: block;
pointer-events: none;
transform: rotate(-90deg);
transition: transform var(--trans-dur) var(--trans-timing);
width: 100%;
height: auto;
}
.timeline__date {
font-size: 0.833em;
line-height: 2.4;
}
.timeline__dot {
background-color: currentColor;
border-radius: 50%;
display: inline-block;
flex-shrink: 0;
margin: 0.625em 0;
margin-inline-end: 1em;
position: relative;
width: 0.75em;
height: 0.75em;
}
.timeline__item {
position: relative;
padding-bottom: 2.25em;
}
.timeline__item:not(:last-child):before {
background-color: currentColor;
content: "";
display: block;
position: absolute;
top: 1em;
left: 2.625em;
width: 0.125em;
height: 100%;
transform: translateX(-50%);
}
[dir="rtl"] .timeline__arrow-icon {
transform: rotate(90deg);
}
[dir="rtl"] .timeline__item:not(:last-child):before {
right: 2.625em;
left: auto;
transform: translateX(50%);
}
.timeline__item-header {
display: flex;
}
.timeline__item-body {
border-radius: 0.375em;
overflow: hidden;
margin-top: 0.5em;
margin-inline-start: 4em;
height: 0;
}
.timeline__item-body-content {
background-color: hsl(var(--hue),10%,50%,0.2);
opacity: 0;
padding: 0.5em 0.75em;
visibility: hidden;
transition:
    opacity var(--trans-dur) var(--trans-timing),
    visibility var(--trans-dur) steps(1,end);
}
.timeline__meta {
width: 100%;
}
.timeline__title {
font-size: 1.5em;
line-height: 1.333;
}
/* Expanded state */
.timeline__item-body--expanded {
height: auto;
}
.timeline__item-body--expanded .timeline__item-body-content {
opacity: 1;
visibility: visible;
transition-delay: var(--trans-dur), 0s;
}
.timeline__arrow[aria-expanded="true"] .timeline__arrow-icon {
transform: rotate(0);
}