Radial gradient shows some return lines, gap, spaces or margins.

Question

I'm new to radial-gradient, and I don't know what are these return lines or spaces between cubes? How to remove them?

* {margin: 0; outline: 0; border: 0;}
.round {
  background: radial-gradient(circle at 0 100%, rgba(204, 0, 0, 0) 70%, #c00 71%),
              radial-gradient(circle at 100% 100%, rgba(204, 0, 0, 0) 70%, #c00 71%), 
              radial-gradient(circle at 100% 0, rgba(204, 0, 0, 0) 70%, #c00 71%), 
              radial-gradient(circle at 0 0, rgba(204, 0, 0, 0) 70%, #c00 71%);
  background-position: bottom left, bottom right, top right, top left;
  background-size: 50% 50%;
  background-repeat: no-repeat;
  width: 300px;
  height: 300px;
  padding: 10%;
  transform: rotate(45deg);
}
p {
  transform: rotate(-45deg);
  width: 100px;
  margin: 100px;
}

<div class="round">
  <p>By using radial gradients, you can simulate rounded corners with a negative radius. Just in this case,</p>
</div>

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Answer 1

There were two problems in your fragment, and when we correct, like those, that the strange gap or line that appears in the middle has completely disappeared.

• 1: padding: 10% . , UA . UA . , , , , 510px, 10% 51px. , 351px, UA 50% background-size, 175.5px. . 175px, FF , , , ... , 350px, 351px, 1px - , .
• 2: . , - , , backface-visibility hidden. . ( Chrome, . , .)

, , . backface-visibility: hidden. , , , . , , , p.

* {
  margin: 0;
  outline: 0;
  border: 0;
}
.round {
  position: relative;
  width: 300px;
  height: 300px;
  padding: 30px;
}
.round:after {
  position: absolute;
  content: '';
  height: 100%;
  width: 100%;
  top: 0px;
  left: 0px;
  background: radial-gradient(circle at 0 100%, rgba(204, 0, 0, 0) 70%, #c00 71%), radial-gradient(circle at 100% 100%, rgba(204, 0, 0, 0) 70%, #c00 71%), radial-gradient(circle at 100% 0, rgba(204, 0, 0, 0) 70%, #c00 71%), radial-gradient(circle at 0 0, rgba(204, 0, 0, 0) 70%, #c00 71%);
  background-position: bottom left, bottom right, top right, top left;
  background-size: 50% 50%;
  background-repeat: no-repeat;
  transform: rotate(45deg);
  backface-visibility: hidden;
  z-index: -1;
}
p {
  width: 125px;
  margin: 85px;
}

<div class="round">
  <p>By using radial gradients, you can simulate rounded corners with a negative radius. Just in this case,</p>
</div>

Hide result

---

vals , 2 . a translateZ(1px) . , .

* {
  margin: 0;
  outline: 0;
  border: 0;
}
.round {
  position: relative;
  width: 300px;
  height: 300px;
  padding: 30px;
  background: radial-gradient(circle at 0 100%, rgba(204, 0, 0, 0) 70%, #c00 71%), radial-gradient(circle at 100% 100%, rgba(204, 0, 0, 0) 70%, #c00 71%), radial-gradient(circle at 100% 0, rgba(204, 0, 0, 0) 70%, #c00 71%), radial-gradient(circle at 0 0, rgba(204, 0, 0, 0) 70%, #c00 71%);
  background-position: bottom left, bottom right, top right, top left;
  background-size: 50% 50%;
  background-repeat: no-repeat;
  transform: rotate(45deg) translateZ(1px);
}
p {
  transform: rotate(-45deg) translateZ(-1px);
  width: 125px;
  margin: 85px;
}

<div class="round">
  <p>By using radial gradients, you can simulate rounded corners with a negative radius. Just in this case,</p>
</div>

Hide result

---

2:

, . vals .

, . , , , 50% . , 50% .

(50% + 50%). 0,5. , 0,5 0.75, 1. , , .

(), Chrome Dev " " " ". , , . , . , 50% .

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Chrome Dev. 3D- (, backface-visibility, translateZ) . ( ), . , , 50-50 . , ( ). ( ).