[Docs] Improve scrollbars (#24971)

Follow dark/light modes.

(cherry picked from commit 9d0c0b8)

Author: AmjadHD

doc/nimdoc.css

@@ -11,6 +11,7 @@ Modified by Boyd Greenfield and narimiran
 */
 
 :root {
+  color-scheme: light;
   --primary-background: #fff;
   --secondary-background: ghostwhite;
   --third-background: #e8e8e8;
@@ -45,6 +46,7 @@ Modified by Boyd Greenfield and narimiran
 }
 
 [data-theme="dark"] {
+  color-scheme: dark;
   --primary-background: #171921;
   --secondary-background: #1e202a;
   --third-background: #2b2e3b;
@@ -80,6 +82,7 @@ Modified by Boyd Greenfield and narimiran
 
 @media (prefers-color-scheme: dark) {
   [data-theme="auto"] {
+    color-scheme: dark;
     --primary-background: #171921;
     --secondary-background: #1e202a;
     --third-background: #2b2e3b;

nimdoc/testproject/expected/nimdoc.out.css

@@ -11,6 +11,7 @@ Modified by Boyd Greenfield and narimiran
 */
 
 :root {
+  color-scheme: light;
   --primary-background: #fff;
   --secondary-background: ghostwhite;
   --third-background: #e8e8e8;
@@ -45,6 +46,7 @@ Modified by Boyd Greenfield and narimiran
 }
 
 [data-theme="dark"] {
+  color-scheme: dark;
   --primary-background: #171921;
   --secondary-background: #1e202a;
   --third-background: #2b2e3b;
@@ -80,6 +82,7 @@ Modified by Boyd Greenfield and narimiran
 
 @media (prefers-color-scheme: dark) {
   [data-theme="auto"] {
+    color-scheme: dark;
     --primary-background: #171921;
     --secondary-background: #1e202a;
     --third-background: #2b2e3b;