Ё CAPITAL LETTER IO UTF-8 character with hex code 0401

Using HEX code of CAPITAL LETTER IO in HTML file

<span> &#x0401; </span>

Using Decimal code of CAPITAL LETTER IO in HTML file

<span> &#1025; </span>

Using HEX code of CAPITAL LETTER IO in CSS file for content

span { 
    content: '\0401';
}