How to use css to implement a page that monitors network connection status

<div class="detector">
    <div class="client"></div>
    <div class="signal"></div>
    <div class="server"></div>
</div>

body {
    margin: 0;
    height: 100vh;
    display: flex;
    align-items: center;
    justify-content: center;
}

:root {
    --status-color: green;
}

body {
    background: linear-gradient(var(--status-color) 5vh, #ccc 5vh);
}

.detector {
    width: 40em;
    height: 14em;
    font-size: 10px;
}

.detector {
    display: flex;
    justify-content: space-between;
    align-items: center;
    color: #333;
}

.detector > * {
    position: relative;
    box-sizing: border-box;
}

.detector > *::before,
.detector > *::after {
    content: '';
    position: absolute;
    box-sizing: border-box;
}

.client {
    width: 17em;
    height: 10em;
    border: 0.5em solid;
    border-radius: 0.5em;
}

.client {
    display: flex;
    flex-direction: column;
    align-items: center;
    margin-top: -4em;
}

.client::before {
    width: 1.5em;
    height: 3em;
    background-color: currentColor;
    top: 9.5em;
}

.client::after {
    width: 5em;
    height: 1em;
    background-color: currentColor;
    border-radius: 0.3em;
    top: 12.5em;
}

.server {
    width: 7em;
    height: 14em;
    border: 0.5em solid;
    border-radius: 0.5em;
}

.server::before {
    width: 5em;
    height: 1em;
    background-color: currentColor;
    border-radius: 0.2em;
    top: 8em;
    left: 0.5em;
    box-shadow: 0 1.5em 0;
}

.server::after {
    width: 0.6em;
    height: 0.6em;
    background-color: currentColor;
    border-radius: 50%;
    right: 1.5em;
    bottom: 0.5em;
    box-shadow: 1em 0 0 0.1em;
}

.signal,
.signal::before,
.signal::after {
    width: 1em;
    height: 1em;
    background-color: var(--status-color);
    border-radius: 50%;
}

.signal::before {
    right: 2.5em;
}

.signal::after {
    left: 2.5em;
}

.signal,
.signal::before,
.signal::after {
    animation: blink 0.6s infinite;
}

@keyframes blink {
    50% {
        filter: opacity(0.1);
    }
}

:root {
    --second-signal-delay: 0.2s;
    --third-signal-delay: 0.4s;
}

.signal::before {
    animation-delay: var(--second-signal-delay);
}

.signal::after {
    animation-delay: var(--third-signal-delay);
}

:root {
    --status-color: green;
    --second-signal-delay: 0.2s;
    --third-signal-delay: 0.4s;
}

:root {
    --status-color: orangered;
    --second-signal-delay: 0s;
    --third-signal-delay: 0s;
}

const ONLINE_THEME = {
    statusColor: 'green',
    secondSignalDelay: '0.2s',
    thirdSignalDelay: '0.4s'
}

const OFFLINE_THEME = {
    statusColor: 'orangered',
    secondSignalDelay: '0s',
    thirdSignalDelay: '0s'
}

function detectOnlineStatus() {
    let theme = navigator.onLine ? ONLINE_THEME : OFFLINE_THEME
    let root = document.documentElement
    root.style.setProperty('--status-color', theme.statusColor)
    root.style.setProperty('--second-signal-delay', theme.secondSignalDelay)
    root.style.setProperty('--third-signal-delay', theme.thirdSignalDelay)
}

detectOnlineStatus()

window.addEventListener('online', detectOnlineStatus)
window.addEventListener('offline', detectOnlineStatus)