Where to find input placeholder style
<p>Couldn't find default placeholder style for input element.
There are no any <code>webkit-input-placeholder</code>, <code>-moz-placeholder</code>, <code>-moz-placeholder</code>, or <code>-ms-input-placeholder</code> style settings in any css files.  </p>

<p>UPDATE: Guys, don't hurry to judge me.
I have the legacy code (tones of css files).  The one placeholder style (font-weight, color and so on) is not properly shown in IE 11. I started to find where the placeholder style is defined. And I didn't find any placeholder style declaration you all mentioned.<br>
So I assume there is a default style for placeholder in browser.</p>