Rewritten in Astro (i had better separate this commit into smaller ones)

src/styles/theme.less

@@ -0,0 +1,42 @@
+@accent: #5070ca;
+
+body {
+    @bg-light: #fff;
+    @fg-light: #202020;
+
+    @bg-dark: #222229;
+    @fg-dark: #eee;
+
+    --accent: @accent;
+
+    .light-mixin() {
+        --bg: @bg-light;
+        --fg: @fg-light;
+        --bg-sec: darken(@bg-light, 30%);
+        --fg-sec: lighten(@fg-light, 15%);
+        --accent-bg: darken(@bg-light, 10%);
+        --accent-hl: darken(@accent, 15%);
+    }
+
+    .dark-mixin() {
+        --bg: @bg-dark;
+        --fg: @fg-dark;
+        --bg-sec: lighten(@bg-dark, 15%);
+        --fg-sec: darken(@bg-light, 25%);
+        --accent-bg: lighten(@bg-dark, 5%);
+        --accent-hl: lighten(@accent, 15%);
+    }
+
+    .dark-mixin();
+    // &.dark {
+    &[data-dark="1"] {
+        .dark-mixin();
+    }
+    // &.light {
+    &[data-dark="0"] {
+        .light-mixin();
+    }
+    @media (prefers-color-scheme: light) {
+        .light-mixin();
+    }
+}