JSFiddle - React, Tailwind, and code Playground

HTML

<!DOCTYPE html>
<html>
    <head>
        <title>Градиент</title>
        <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
        <link rel="stylesheet" type="text/css" href="style3.css" />
    </head>
    <body>
        <div id="wrapper">
            <div id="inner">
                <div id="header">
                    Заголовок <div id="triangle"></div>
                </div>
                <div id="content">
                    Содержимое
                </div>
            </div>
        </div>
    </body>
</html>

CSS

html, body, div{
    margin:0;
    padding:0;
    background: transparent;
    outline: 0;
    border: 0;
    font-family: sans-serif;
}

body{
    background-color: #FFF;
}

#wrapper{
    margin: 10px;
    padding: 10px;
    border: 2px solid #004C3B;
    background: -webkit-gradient(
        linear,
        left bottom,
        left top,
        color-stop(0, rgb(91,146,108,0.6)),
        color-stop(1, rgb(97,203,178,0.6))
    );
    background: -moz-linear-gradient(
        center bottom,
        rgba(91,146,108,0.6) 0%,
        rgba(97,203,178,0.6) 100%
    );
    
    border: 1px solid #000; 
    border-radius: 5px;
    -moz-border-radius: 5px;
    -webkit-border-radius: 5px;
}

#inner{
    background: transparent;
}

#header{
    padding: 8px;
    border: 1px solid #000; 
    border-bottom: 0;
    border-radius: 5px 5px 0 0;
    -moz-border-radius: 5px 5px 0 0;
    -webkit-border-radius: 5px 5px 0 0;
    background: -webkit-gradient(
        linear,
        left bottom,
        left top,
        color-stop(0.3, rgb(255,187,0)),
        color-stop(1, rgb(255,217,0))
    );
    background: -moz-linear-gradient(
        center bottom,
        rgb(255,187,0) 30%,
        rgb(255,217,0) 100%
    );
}

#content{
    background-color: #FFF;
    border: 1px solid #000; 
    border-top: 0;
    border-radius: 0 0 5px 5px;
    -moz-border-radius: 0 0 5px 5px;
    -webkit-border-radius: 0 0 5px 5px;
    padding: 10px;
    font-size: 0.9em;
}