Selenium Compound Class Name [unable to insert a value]

I am currently having a hard time inserting a value into a field which is within a Frame, I have tried removing the spaces in the class name but it didn't work

class="ng-pristine ng-valid ng-scope ng-empty input-sm form-control nc-pristine ng-valid-required ng-touched"

<textarea ng-if="$ctrl.fieldType.isTextarea($ctrl.field.fieldType, $ctrl.field.isHtmlFormatted)" ng-model="$ctrl.field.value" ng-change="$ctrl.onChange()" ng-required="$ctrl.field.isRequired" ng-class="{
    'input-sm': true,
    'form-control': true,
    'nc-pristine': $ctrl.getPristine(),
    'nc-not-pristine': $ctrl.getNotPristine()
   }" class="ng-pristine ng-valid ng-scope ng-empty input-sm form-control nc-pristine ng-valid-required ng-touched"></textarea>

I have tried in Chrome Developer tool and it worked with this javascript code

Chrome Console Developper Javascript

document.getElementsByClassName('ng-pristine ng-valid ng-scope ng-empty input-sm form-control nc-pristine ng-valid-required ng-touched')[0].value='Hello World';

In Selenium I tried with these 2 ways none of them work:

Using Javascript

IJavaScriptExecutor js = (IJavaScriptExecutor)driver;
js.ExecuteScript("document.getElementsByClassName('ng-pristine ng-valid ng-scope ng-empty input-sm form-control nc-pristine ng-valid-required ng-touched')[0].value='Hello World';");

Error Message:

 System.InvalidOperationException occurred
  HResult=0x80131509
  Message=unknown error: Cannot set property 'value' of undefined
  (Session info: chrome=62.0.3202.94)
  (Driver info: chromedriver=2.33.506120 (e3e53437346286c0bc2d2dc9aa4915ba81d9023f),platform=Windows NT 10.0.15063 x86_64)
  Source=WebDriver
  StackTrace:
   at OpenQA.Selenium.Remote.RemoteWebDriver.UnpackAndThrowOnError(Response errorResponse)
   at OpenQA.Selenium.Remote.RemoteWebDriver.Execute(String driverCommandToExecute, Dictionary`2 parameters)
   at OpenQA.Selenium.Remote.RemoteWebDriver.ExecuteScriptCommand(String script, String commandName, Object[] args)
   at OpenQA.Selenium.Remote.RemoteWebDriver.ExecuteScript(String script, Object[] args)
   at ConsoleApp5.Program.Main(String[] args) 

Using cssSelector, removing the spacing in the Class Name and replacing it with dots

driver.FindElement(By.CssSelector("ng-pristine.ng-valid.ng-scope.ng-empty.input-sm.form-control.nc-pristine.ng-valid-required.ng-touched")).SendKeys("Hello World");

Error Message

  OpenQA.Selenium.NoSuchElementException occurred
  HResult=0x80131500
  Message=no such element: Unable to locate element: {"method":"css selector","selector":"ng-pristine.ng-valid.ng-scope.ng-empty.input-sm.form-control.nc-pristine.ng-valid-required.ng-touched"}
  (Session info: chrome=62.0.3202.94)
  (Driver info: chromedriver=2.33.506120 (e3e53437346286c0bc2d2dc9aa4915ba81d9023f),platform=Windows NT 10.0.15063 x86_64)
  Source=WebDriver
  StackTrace:
   at OpenQA.Selenium.Remote.RemoteWebDriver.UnpackAndThrowOnError(Response errorResponse)
   at OpenQA.Selenium.Remote.RemoteWebDriver.Execute(String driverCommandToExecute, Dictionary`2 parameters)
   at OpenQA.Selenium.Remote.RemoteWebDriver.FindElement(String mechanism, String value)
   at OpenQA.Selenium.Remote.RemoteWebDriver.FindElementByCssSelector(String cssSelector)
   at OpenQA.Selenium.By.<>c__DisplayClass23_0.<CssSelector>b__0(ISearchContext context)
   at OpenQA.Selenium.By.FindElement(ISearchContext context)
   at OpenQA.Selenium.Remote.RemoteWebDriver.FindElement(By by)

Given the html provided try this:

driver.findElement(By.cssSelector("div > div > nc-editable-field > textarea"));

Also, you stated that the element is in Frame, are you sure that you are switching to that frame correctly?