The below might give you an idea of how to proceed .. maybe use some css like the calc()
to find the right sizes so that you don't set them statically
.ct-golden-section:before {
display: block;
float: left;
content: "";
width: 100%;
height: 413px; //set as the size of the container
padding-bottom: 449px; //set as the size of the container
background: yellow; // set the bg color wanted for the container
border-style: solid;
border-top-width: 15px;
border-left-width: 49px;
border-color: orange; // choose the color of the page u have
border-bottom-width: 25px;
border-right-width: 39px;
}
Check the screenshot to see the result of the above:
https://drive.google.com/file/d/15-vuRMXn2NspkNWfIuvcEZ8xxOEUeEgd/view?usp=sharing
Please anyone feel free to edit my temporary solution