htmlcssborder-radius

How to adjust border radius to match parent border radius

I want to have a text box with a line on the left side for design purpouses. The box has a border radius oh 10px. The problem is that the line is too thick if I make it 10px wide. So I made it 5px and tried to adjust the horizontal and vertical radiuses separately to make it match the border of the box. I have tried for ages and I just cant get it right. Here's my best attempt:

div {
  position: relative;
  width: 400px;
  height: 200px;
  background-color: rgba(0, 255, 50, 0.3);
  border-radius: 10px;
}

div::before {
  content: "";
  position: absolute;
  top: 50%;
  -webkit-transform: translateY(-50%);
  -ms-transform: translateY(-50%);
  transform: translateY(-50%);
  left: 0;
  width: 5px;
  height: calc(100% - 3px);
  background-color: rgba(0, 150, 0, 0.5);
  border-radius: 5px 0 0 5px / 10px 0 0 10px;
}

p {
  position: absolute;
  top: 40%;
  left: 35%;
}
<div>
  <p>Make me beautiful!</p>
</div>

Is it even possible to make this work and how?

Edit: I'm using the same variable for the background color of the line and the box. Then I'm applying a filter to the line to make it darker.

Solution

  • If it's only for decoration, use a gradient:

    div {
  position: relative;
  width: 400px;
  height: 200px;
  background: 
   linear-gradient(rgba(0, 150, 0, 0.5) 0 0) /* color */
     left / 5px 100% no-repeat, /* position / width height */
   rgba(0, 255, 50, 0.3);
  border-radius: 10px;
}

p {
  position: absolute;
  top: 40%;
  left: 35%;
}
    <div>
  <p>Make me beautiful!</p>
</div>