Hola! Amigos de aprenderaprogramar.
Dejo la respuesta al ejercicio propuesto en el capítulo CU01061D del curso de css desde cero:
Código:
<!DOCKTYPE html>
<head>
<meta charset="utf-8">
<meta name="description" content="Tema 1061 radial-gradient">
<meta name="keywords" content="palabras clave">
<title>Tema 1059 Radial-gradient</title>
<style type="text/css">
*{margin:0; padding:0; font-family:'Snap ITC', sans-serif;}
div{width:400px; height:200px;}
#div1{width:460px; height:260px;
background-image:url(https://encrypted-tbn3.gstatic.com/images?q=tbn:ANd9GcR4gtgWpjM_X5cR8b2TM6llbpCvTztaE8-I8f-HmMfDqUWIH7mS);
background-position:center;}
#div2{background:radial-gradient(rgba(255,0,0,0), rgba(255,0,0,1));
border:30px solid;
border-image-source:url(data:image/jpeg;base64,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);
border-image-slice:17;}
</style>
</head>
<body>
<div id="div1"><div id="div2"></div></div>
</body>
</html>
Un saludo!
Y gracias por vuestro trabajo.