Fix SVG visibility in dark mode

Invert SVG colors in dark mode to improve visibility. Also, override
OS-level dark mode when the site is in light mode to ensure the correct
theme is used.

assets/css/custom.css

@@ -0,0 +1,23 @@
+/* Fix SVG visibility in dark mode by inverting colors */
+.dark svg {
+    filter: invert(1) hue-rotate(180deg);
+}
+
+/* Counter-invert images within SVGs to preserve their original colors */
+.dark svg image {
+    filter: invert(1) hue-rotate(180deg);
+}
+
+/* Fix tech-banner gradient overlays to respect site theme, not OS theme */
+:root {
+    --color-bg: #ffffff;
+}
+
+.dark {
+    --color-bg: #111111 !important;
+}
+
+/* Override OS-level dark mode when site is in light mode */
+html:not(.dark) {
+    --color-bg: #ffffff !important;
+}