Helping developers find appropriate information about how to apply a custom theme to site collections programmatically. (SharePoint#2374)

* Update sharepoint-site-theming-overview.md

Adding reference to (current) appropriate way to apply custom themes to site collections programmatically.

* Update sharepoint-site-theming-csom.md

Making information about how you can apply custom themes to a site collection more findable.

Author: juliemturner

docs/declarative-customization/site-theming/sharepoint-site-theming-csom.md

@@ -79,7 +79,7 @@ public class SPOTheme 
 
 ## Applying a theme
 
-There's currently no supported API to programmatically apply a theme to a specific site.
+There's currently no supported CSOM API to programmatically apply a theme to a specific site. For information on applying custom themes to individual site collections see [SharePoint site design and site script overview](https://docs.microsoft.com/en-us/sharepoint/dev/declarative-customization/site-design-overview)
 
 ## Methods/properties of the Microsoft.Online.SharePoint.TenantAdministration.Tenant class
 

docs/declarative-customization/site-theming/sharepoint-site-theming-overview.md

@@ -16,7 +16,7 @@ These new features include:
 * An updated color palette, with 12 light colors and 6 dark colors, as well as 16 supplementary themes.
 * Control over which themes are available for use on pages within your sites. For example, you can define custom themes based on your organization's branding or identity, and make those the only available themes within your sites.
 
-These capabilities are available to administrators via [PowerShell cmdlets](sharepoint-site-theming-powershell.md), and to developers via the [SharePoint client-side object model (CSOM)](sharepoint-site-theming-csom.md) or the [SharePoint REST API](sharepoint-site-theming-rest-api.md).
+These capabilities are available to administrators via [PowerShell cmdlets](sharepoint-site-theming-powershell.md), and to developers via the [SharePoint client-side object model (CSOM)](sharepoint-site-theming-csom.md) or the [SharePoint REST API](sharepoint-site-theming-rest-api.md). For information on applying custom themes to individual site collections see [SharePoint site design and site script overview](https://docs.microsoft.com/en-us/sharepoint/dev/declarative-customization/site-design-overview)
 
 For general information about working with themes to customize the look of your sites, see [Change the look of your SharePoint site](https://support.office.com/en-us/article/Change-the-look-of-your-SharePoint-site-06bbadc3-6b04-4a60-9d14-894f6a170818).