set a width of fixed positioned div relative to its sibling div and parent?

I wanted to set a width of a fixed div as the image resizes

let’s have a look at the h&m website product page i’ve been examining

https://www2.hm.com/en_us/productpage.0658859005.html

container
  --figure 
  -- product-detail-info - it should be fixed as scrolling

on this page, when you scroll the property of ‘position’ of ‘product-detail-info’ switch to the ‘fixed’

it means

.container{width:100%}
  .stiky-wrapper{ width:max-width: calc(100vw - 505px);
                  width: 66%; 
                  width: calc(66vw - 2 * 40px); }
     figure{position:relative}
     .product-detail-info{ 
                  position:absolute;
                  top:0;
                  left:100%;
                  width: calc( 34vw - 17px ) !important;
                  min-width: 408px; }

• left:100% — it seems that the left content follow the image as resizing

position-absolute

#the position changes as scrolling

.product-detail-info{
  position: fixed;
  top: 40px;
  min-width: 408px;
  left: calc(100vw - 465px);
}

position-fixed

I just wanted to find out not to use javascript.

look at below what I’ve done without javascript!

#reference

https://css-tricks.com/forums/topic/width-fixed-div-element-same-as-the-parents/