1<button
2 class="theme-toggle"
3 aria-pressed="true">
4   <!-- A whole lotta SVG -->
5   <span class="sr-only">Toggle theme</span>
6</button>

1.theme-toggle {
2  container-type: inline-size;
3}
4.theme-toggle__indicator {
5  transition: translate var(--speed) var(--slide-ease);
6  translate: calc(var(--dark, 0) * (100cqi - 100%)) 0;
7}
8.theme-toggle[aria-pressed=true] {
9	--dark: 1;
10}