[css-forms-1] Add textarea to pseudo elements table

Also add placeholder pseudo to definitions

Author: lukewarlow

css-forms-1/Overview.bs

@@ -254,6 +254,10 @@ Markup Shorthands: css yes, markdown yes
         <td>`<input type=color>`</td>
         <td>''::color-swatch''</td>
       </tr>
+      <tr>
+        <td>`<textarea>`</td>
+        <td>See [[#textarea-pseudos]]</td>
+      </tr>
       <tr>
         <td>`<select>`</td>
         <td>''::picker-icon''</td>
@@ -370,6 +374,11 @@ Markup Shorthands: css yes, markdown yes
 ## Styling Parts for Text Fields: the ''::field-text'' and ''::clear-icon'' pseudo-elements ## {#field-pseudos}
 
   <dl export>
+    <dt><dfn>''::placeholder''</dfn>
+    <dd>
+      The ''::placeholder'' pseudo-element represents
+      the portion of the <{input}> that contains the placeholder text.
+
     <dt><dfn>::field-text</dfn>
     <dd>
       The ''::field-text'' pseudo-element represents
@@ -385,11 +394,35 @@ Markup Shorthands: css yes, markdown yes
       With ''appearance: textfield'', the user agent must not generate this part.
   </dl>
 
-  ''::field-text'' and ''::clear-icon'' must be siblings.
+  ''::placeholder'', ''::field-text'' and ''::clear-icon'' must be siblings.
 
   ISSUE: Collect parts used by autofill.
 
-  ISSUE: Define something for the password visibility toggle for user agents implementing it?
+  ISSUE(11845): Define something for the password visibility toggle for user agents implementing it?
+
+## Styling Parts for textareas: the ''::placeholder'' and ''::field-text'' pseudo-elements ## {#textarea-pseudos}
+
+  <dl export>
+    <dt><span>''::placeholder''</span>
+    <dd>
+      The ''::placeholder'' pseudo-element represents
+      the portion of the <{textarea}> that contains the placeholder text.
+
+    <dt><span>''::field-text''</span>
+    <dd>
+      The ''::field-text'' pseudo-element represents
+      the portion of the <{textarea}> that contains the editable text.
+  </dl>
+
+  Their structure is defined as follows:
+
+    ```
+        <textarea>
+        ├─ ::placeholder
+        └─ ::field-text
+    ```
+
+  ISSUE(11850): Define something for the resizer.
 
 ## Styling Parts for Number Fields: the ''::step-control'', ''::step-up'' and ''::step-down'' pseudo-elements ## {#number-pseudos}