Initial support for colorblindness-friendly themes (#30625)

Initial support for #25680

This PR only adds some simple styles from GitHub, it is big enough and
it focuses on adding the necessary framework-level supports. More styles
could be fine-tuned later.

services/forms/user_form.go

@@ -11,7 +11,6 @@ import (
 
 	auth_model "code.gitea.io/gitea/models/auth"
 	user_model "code.gitea.io/gitea/models/user"
-	"code.gitea.io/gitea/modules/setting"
 	"code.gitea.io/gitea/modules/structs"
 	"code.gitea.io/gitea/modules/web/middleware"
 	"code.gitea.io/gitea/services/context"
@@ -273,7 +272,7 @@ func (f *AddEmailForm) Validate(req *http.Request, errs binding.Errors) binding.
 
 // UpdateThemeForm form for updating a users' theme
 type UpdateThemeForm struct {
-	Theme string `binding:"Required;MaxSize(30)"`
+	Theme string `binding:"Required;MaxSize(255)"`
 }
 
 // Validate validates the field
@@ -282,20 +281,6 @@ func (f *UpdateThemeForm) Validate(req *http.Request, errs binding.Errors) bindi
 	return middleware.Validate(errs, ctx.Data, f, ctx.Locale)
 }
 
-// IsThemeExists checks if the theme is a theme available in the config.
-func (f UpdateThemeForm) IsThemeExists() bool {
-	var exists bool
-
-	for _, v := range setting.UI.Themes {
-		if strings.EqualFold(v, f.Theme) {
-			exists = true
-			break
-		}
-	}
-
-	return exists
-}
-
 // ChangePasswordForm form for changing password
 type ChangePasswordForm struct {
 	OldPassword string `form:"old_password" binding:"MaxSize(255)"`