theme switcher

src/components/Icon.astro

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+---
+export interface Props {
+    name: string,
+};
+
+const { name } = Astro.props;
+
+const icons = import.meta.glob<{string: string}>('@components/icons/*.svg', { query: '?raw', import: 'default' });
+const path = `/src/components/icons/${name}.svg`;
+if (icons[path] === undefined) {
+    throw new Error(`Icon ${name} does not exist.`);
+}
+const icon = await icons[path]();
+---
+
+<Fragment set:html={icon} />
+
+<style>
+    svg {
+        width: 100%;
+        height: 100%;
+    }
+</style>

src/components/ThemeSwitcher.astro

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+---
+import Icon from '@components/Icon.astro';
+---
+
+
+<div class="theme-switcher">
+    <button id="switch-to-dark">
+        <Icon name="sun" />
+    </button>
+    <button id="switch-to-light">
+        <Icon name="moon" />
+    </button>
+</div>
+
+
+<style>
+.theme-switcher {
+    position: relative;
+    isolation: isolate;
+    width: 1.5rem;
+    height: 1.5rem;
+
+    transform: translateY(0.1rem);
+}
+
+button {
+    position: absolute;
+    inset: 0;
+
+    background-color: transparent;
+    padding: 0;
+    color: var(--nav-link-color);
+    border: none;
+
+    &:hover {
+        cursor: pointer;
+        color: var(--accent-color);
+    }
+
+    /* hide by default, i.e. if JS isn't enabled and the data-theme attribute didn't get set, */
+    visibility: hidden;
+    opacity: 0;
+    transition:
+        color 0.2s ease,
+        opacity 0.5s ease,
+        transform 0.5s ease;
+}
+
+:global(html[data-theme="light"]) button#switch-to-dark {
+    opacity: 1;
+    visibility: visible;
+    transform: rotate(360deg);
+    /* whichever one is currently active should be on top */
+    z-index: 10;
+}
+:global(html[data-theme="dark"]) button#switch-to-light {
+    opacity: 1;
+    visibility: visible;
+    transform: rotate(-360deg);
+    z-index: 10;
+}
+</style>
+
+<script>
+document.getElementById('switch-to-dark')?.addEventListener('click', () => {
+    localStorage.setItem('theme-preference', 'dark');
+    document.documentElement.dataset.theme = 'dark';
+});
+document.getElementById('switch-to-light')?.addEventListener('click', () => {
+    localStorage.setItem('theme-preference', 'light');
+    document.documentElement.dataset.theme = 'light';
+})
+</script>

src/components/icons/moon.svg

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+<svg xmlns="http://www.w3.org/2000/svg" fill="none" viewBox="0 0 24 24" stroke-width="1.5" stroke="currentColor">
+  <path stroke-linecap="round" stroke-linejoin="round" d="M21.752 15.002A9.72 9.72 0 0 1 18 15.75c-5.385 0-9.75-4.365-9.75-9.75 0-1.33.266-2.597.748-3.752A9.753 9.753 0 0 0 3 11.25C3 16.635 7.365 21 12.75 21a9.753 9.753 0 0 0 9.002-5.998Z" />
+</svg>
+
+<style>
+svg {
+    width: 100%;
+    height: 100%;
+}
+</style>

src/components/icons/sun.svg

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+<svg xmlns="http://www.w3.org/2000/svg" fill="none" viewBox="0 0 24 24" stroke-width="1.5" stroke="currentColor">
+  <path stroke-linecap="round" stroke-linejoin="round" d="M12 3v2.25m6.364.386-1.591 1.591M21 12h-2.25m-.386 6.364-1.591-1.591M12 18.75V21m-4.773-4.227-1.591 1.591M5.25 12H3m4.227-4.773L5.636 5.636M15.75 12a3.75 3.75 0 1 1-7.5 0 3.75 3.75 0 0 1 7.5 0Z" />
+</svg>