After analyzing the scenario presented, it appears that the outer yellow box is 240px wide (200 width plus 20 padding on each side).
The red child inside has its width set at 50%. Surprisingly, when rendered, the red box measures 140px in width. You can view the image here.
There seems to be confusion regarding how this value is calculated. It's expected that the child's width should align with the parent's padding if accounted for, resulting in 100 (50% of 200). Alternatively, factoring in the padding could lead to a width of 120 (50% of 240), rather than the observed 140...
When setting the child's width to 100%, the box expands to 240px. Refer to the image here.
This suggests that the padding is included in the calculation process (100% of 240 equals 240). Logically, 50% should result in 120 (50% of 240), yet it yields 140.
According to the browser, 100% of 240 constitutes 240 and 50% equates to 140. Quite perplexing!
It appears there might be a specific formula at play here, but unfortunately, I haven't come across any documented details.
The CSS styles pertaining to the elements are as follows:
div {
background-color: yellow;
padding-left: 20px;
padding-right: 20px;
width: 200px;
height: 200px;
}
div.child {
background-color: red;
width: 50%;
height: 50%;
}
Thank you for your help!