Hi,
See the WordPress support document for how to setup a child theme.
You must reference the master theme from the child theme, it will work fine.
Here is the code I have so far, you can start with that and change it as needed.
/*
Theme Name: Duena Child
Theme URI: https://zypath.com/wp-content/themes/duena-child
Description: Duena Child Theme
Author: Chuck Bunn
Author URI: https://zypath.com
Template: duena
Version: 1.0.0
*/
@import url("../duena/style.css");
/* YouTube container for responsive theme
----------------------------------------------- */
.video-container {
position: relative;
padding-bottom: 56.25%;
padding-top: 30px;
height: 0;
overflow: hidden;
}
.video-container iframe,
.video-container object,
.video-container embed {
position: absolute;
top: 0;
left: 0;
width: 100%;
height: 100%;
}
/* Post date color on white background
----------------------------------------------- */
.post_date time {
color: #434242;
}
/* Turn of Related post display
----------------------------------------------- */
.related-posts {
display: none;
}
/* Tag Cloud colors
----------------------------------------------- */
.tagcloud a {
background: #ffffff;
color: #ff5b5b;
border: 1px solid #8b8686;
}
Hope that helps