chore: improve onboarding, app download links styling (#23134)

web/src/routes/auth/onboarding/+page.svelte

@@ -90,7 +90,7 @@
       component: OnboardingMobileApp,
       role: OnboardingRole.USER,
       title: $t('mobile_app'),
-      icon: mdiCellphoneArrowDownVariant, // or you can use mdiCellphone
+      icon: mdiCellphoneArrowDownVariant,
     },
   ]);
 
@@ -167,7 +167,7 @@
         style="width: {(onboardingProgress / onboardingStepCount) * 100}%"
       ></div>
     </div>
-    <div class="py-8 flex place-content-center place-items-center m-auto">
+    <div class="py-8 flex place-content-center place-items-center m-auto w-[min(100%,_800px)]">
       <OnboardingCard
         title={onboardingSteps[index].title}
         icon={onboardingSteps[index].icon}