Stacking circles produces a black bar on border radius

Question

I have quite the puzzling enterprise here.

I'm building a mouse which serves as a 'torch / searchlight'. All text (inline elements, buttons, you get the point) gets inverted from the usual white to black if there is a hover happening on it, the normal background is a yellow-ish vibe.

I currently have the following setup:

const _$shadow = $('.b-cursor__shadow');
const _$front = $('.b-cursor__front');
const _$back = $('.b-cursor__back');

$(document).on('mousemove', (e) => {
  _$back.css({
    left: e.pageX,
    top: e.pageY
  });
  _$front.css({
    left: e.pageX,
    top: e.pageY
  });
  _$shadow.css({
    left: e.pageX,
    top: e.pageY
  });
});

html,
body {
  padding: 0;
  margin: 0;
  cursor: none;
  background: red;
}

.test {
  background: darkblue;
}

p {
  color: white;
  font-family: sans-serif;
  font-size: 20px;
  max-width: 30rem;
  padding: 1rem;
  margin: 1rem;
  border: 1px solid white;
}

p,
span,
a {
  position: relative;
  z-index: 105;
}

.b-cursor__back,
.b-cursor__front,
.b-cursor__shadow {
  position: fixed;
  width: 8rem;
  height: 8rem;
  margin-left: -4rem;
  margin-top: -4rem;
  border-radius: 50%;
}

.b-cursor__shadow {
  box-shadow: 0px 0px 10px 10px rgba(231, 232, 192, 1);
}

/* background changes */
.b-cursor__back {
  z-index: 104;
  background: #18173e;
  clip-path: circle(50% at 50% 50%);
}

.b-cursor__front {
  z-index: 106;
  background: white;
  clip-path: circle(50% at 50% 50%);
  mix-blend-mode: difference;
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>

<p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Duis pretium pharetra ipsum, at placerat ante maximus vitae. Duis lacus urna, posuere id dapibus in, semper vitae massa. Quisque at egestas nisl. In ex elit, imperdiet eu interdum a, auctor vitae ante. Pellentesque efficitur imperdiet elementum. Integer at nibh gravida nisl sodales ornare ut quis est. Suspendisse sem odio, congue vitae felis at, tincidunt interdum purus. Morbi vitae efficitur est, non congue ante. Proin vel odio et metus sodales lobortis quis ut justo. Phasellus rhoncus eu urna vitae tristique. Suspendisse potenti. Curabitur quis quam lobortis mi laoreet lacinia. Cras non ultrices eros. Nam sed leo et tortor vestibulum cursus nec eu massa. Suspendisse potenti.</p>

<section class="b-cursor">
  <div class="b-cursor__shadow"></div>
  <div class="b-cursor__back"></div>
  <div class="b-cursor__front"></div>
</section>
<div class="test">
  <p>ja uh misschien werkt dit wel niet
    <p>
</div>

(codepen)

This nearly produces the desired result, except the border-radius: 50% doesn't handle semi-nice stacking divs correctly. Pixel drama! Image for clarification:

Question: How can I remove the black border created by stacking these two elements with identical size while preserving the current effect on text?

Answer 1

I would simply add another element above using pseudo element to hide that small border and simplify the code by moving the container instead of each element. Also no need for the clip-path

const _$cursor = $('.b-cursor');

$(document).on('mousemove', (e) => {
  _$cursor.css({
    left: e.pageX,
    top: e.pageY
  });
});

html,
body {
  padding: 0;
  margin: 0;
  cursor: none;
  background: red;
}

.test {
  background: darkblue;
}

p {
  color: white;
  font-family: sans-serif;
  font-size: 20px;
  max-width: 30rem;
  padding: 1rem;
  margin: 1rem;
  border: 1px solid white;
}

p,
span,
a {
  position: relative;
  z-index: 105;
}

.b-cursor { /*no z-index here !!!*/
  position: absolute;
  width: 8rem;
  height: 8rem;
  margin-left: -4rem;
  margin-top: -4rem;
}
/*the magic element*/
.b-cursor:before {
  content:"";
  position:absolute;
  top:-1px;
  left:-1px;
  right:-1px;
  bottom:-1px;
  border:2px solid rgba(231, 232, 192, 1);
  border-radius:50%;
  z-index:999;
}
/**/

.b-cursor__back,
.b-cursor__front,
.b-cursor__shadow {
  position:absolute;
  top:0;
  left:0;
  width:100%;
  height:100%;
  border-radius: 50%;
}

.b-cursor__shadow {
  box-shadow: 0px 0px 10px 10px rgba(231, 232, 192, 1);
}

/* background changes */
.b-cursor__back {
  z-index: 104;
  background: #18173e;
}

.b-cursor__front {
  z-index: 106;
  background: white;
  mix-blend-mode: difference;
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>

<p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Duis pretium pharetra ipsum, at placerat ante maximus vitae. Duis lacus urna, posuere id dapibus in, semper vitae massa. Quisque at egestas nisl. In ex elit, imperdiet eu interdum a, auctor vitae ante. Pellentesque efficitur imperdiet elementum. Integer at nibh gravida nisl sodales ornare ut quis est. Suspendisse sem odio, congue vitae felis at, tincidunt interdum purus. Morbi vitae efficitur est, non congue ante. Proin vel odio et metus sodales lobortis quis ut justo. Phasellus rhoncus eu urna vitae tristique. Suspendisse potenti. Curabitur quis quam lobortis mi laoreet lacinia. Cras non ultrices eros. Nam sed leo et tortor vestibulum cursus nec eu massa. Suspendisse potenti.</p>

<section class="b-cursor">
  <div class="b-cursor__back"></div>
  <div class="b-cursor__front"></div>
  <div class="b-cursor__shadow"></div>
</section>
<div class="test">
  <p>ja uh misschien werkt dit wel niet</p>
</div>

Here is anoher idea with less of code and pure JS without jQuery:

document.onmousemove = function(e) {
  document.body.style.setProperty('--mx',(e.pageX)+'px');
  document.body.style.setProperty('--my',(e.pageY)+'px');
  
  document.body.style.setProperty('--x',(e.clientX)+'px');
  document.body.style.setProperty('--y',(e.clientY)+'px');
  

}

html {
  background:red;
}
body{
  padding: 1px;
  margin: 0;
  min-height:100vh;
  cursor: none;
  background:
    radial-gradient(circle at var(--x) var(--y),#18173e 4rem,transparent 4rem) fixed;
}

.test {
  background:
    radial-gradient(circle at var(--x) var(--y),#18173e 4rem,transparent 4rem) fixed,
    darkblue;
}

p {
  color: white;
  font-family: sans-serif;
  font-size: 20px;
  max-width: 30rem;
  padding: 1rem;
  margin: 1rem;
  border: 1px solid white;
}

.b-cursor { /*no z-index here !!!*/
  position: absolute;
  width: 8rem;
  height: 8rem;
  top:var(--my);
  left:var(--mx);
  margin-left: -4rem;
  margin-top: -4rem;
}
/*the magic element*/
.b-cursor:before{
  content:"";
  position:absolute;
  top:-1px;
  left:-1px;
  right:-1px;
  bottom:-1px;
  border:2px solid rgba(231, 232, 192, 1);
  border-radius:50%;
  z-index:999;
}
.b-cursor:after {
  content:"";
  position:absolute;
  top:0;
  left:0;
  right:0;
  bottom:0;
  box-shadow: 0px 0px 10px 10px rgba(231, 232, 192, 1);
  border-radius:50%;
  z-index:998;
}
/**/
.b-cursor > div {
  position:absolute;
  top:0;
  left:0;
  width:100%;
  height:100%;
  border-radius: 50%;
  z-index: 997;
  background: white;
  mix-blend-mode: difference;
}

<p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Duis pretium pharetra ipsum, at placerat ante maximus vitae. Duis lacus urna, posuere id dapibus in, semper vitae massa. Quisque at egestas nisl. In ex elit, imperdiet eu interdum a, auctor vitae ante. Pellentesque efficitur imperdiet elementum. Integer at nibh gravida nisl sodales ornare ut quis est. Suspendisse sem odio, congue vitae felis at, tincidunt interdum purus. Morbi vitae efficitur est, non congue ante. Proin vel odio et metus sodales lobortis quis ut justo. Phasellus rhoncus eu urna vitae tristique. Suspendisse potenti. Curabitur quis quam lobortis mi laoreet lacinia. Cras non ultrices eros. Nam sed leo et tortor vestibulum cursus nec eu massa. Suspendisse potenti.</p>

<section class="b-cursor">
  <div></div>
</section>
<div class="test">
  <p>ja uh misschien werkt dit wel niet</p>
</div>

You can still optimize more if we consider another gradient that will replace the shadow and the border that we used to fix the black one:

document.onmousemove = function(e) {
  document.body.style.setProperty('--mx',(e.pageX)+'px');
  document.body.style.setProperty('--my',(e.pageY)+'px');
  
  document.body.style.setProperty('--x',(e.clientX)+'px');
  document.body.style.setProperty('--y',(e.clientY)+'px');
  

}

html {
  background:red;
}
body{
  padding: 1px;
  margin: 0;
  min-height:100vh;
  cursor: none;
  background:
    radial-gradient(circle at var(--x) var(--y),#18173e 4rem,transparent 4rem) fixed;
}

.test {
  background:
    radial-gradient(circle at var(--x) var(--y),#18173e 4rem,transparent 4rem) fixed,
    darkblue;
}

p {
  color: white;
  font-family: sans-serif;
  font-size: 20px;
  max-width: 30rem;
  padding: 1rem;
  margin: 1rem;
  border: 1px solid white;
}

.b-cursor { /*no z-index here !!!*/
  position: absolute;
  width: 8rem;
  height: 8rem;
  top:var(--my);
  left:var(--mx);
  margin-left: -4rem;
  margin-top: -4rem;
}

.b-cursor:before{
  content:"";
  position:absolute;
  top:-10px;
  left:-10px;
  right:-10px;
  bottom:-10px;
  background:
    radial-gradient(farthest-side, 
      transparent calc(100% - 18px),rgba(231, 232, 192, 1) calc(100% - 15px),
      rgba(231, 232, 192, 1) calc(100% - 10px),transparent 100%);
  border-radius:50%;
  z-index:999;
}

.b-cursor:after {
  content:"";
  position:absolute;
  top:0;
  left:0;
  width:100%;
  height:100%;
  border-radius: 50%;
  z-index: 998;
  background: white;
  mix-blend-mode: difference;
}

<p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Duis pretium pharetra ipsum, at placerat ante maximus vitae. Duis lacus urna, posuere id dapibus in, semper vitae massa. Quisque at egestas nisl. In ex elit, imperdiet eu interdum a, auctor vitae ante. Pellentesque efficitur imperdiet elementum. Integer at nibh gravida nisl sodales ornare ut quis est. Suspendisse sem odio, congue vitae felis at, tincidunt interdum purus. Morbi vitae efficitur est, non congue ante. Proin vel odio et metus sodales lobortis quis ut justo. Phasellus rhoncus eu urna vitae tristique. Suspendisse potenti. Curabitur quis quam lobortis mi laoreet lacinia. Cras non ultrices eros. Nam sed leo et tortor vestibulum cursus nec eu massa. Suspendisse potenti.</p>

<section class="b-cursor">
</section>
<div class="test">
  <p>ja uh misschien werkt dit wel niet</p>
</div>

---

Safari doesn't support the gradient syntax with at as detailed in this question so here is another alternative:

document.onmousemove = function(e) {
  document.body.style.setProperty('--mx',(e.pageX)+'px');
  document.body.style.setProperty('--my',(e.pageY)+'px');
  
  document.body.style.setProperty('--x',(e.clientX)+'px');
  document.body.style.setProperty('--y',(e.clientY)+'px');
  

}

html {
  background:red;
}
body{
  padding: 1px;
  margin: 0;
  min-height:100vh;
  cursor: none;
  background:
    radial-gradient(farthest-side ,#18173e 100%,transparent 100%)
    calc(var(--x) - 4rem) calc(var(--y) - 4rem)/8rem 8rem  fixed no-repeat;
}

.test {
  background:
    radial-gradient(farthest-side ,#18173e 100%,transparent 100%)
    calc(var(--x) - 4rem) calc(var(--y) - 4rem)/8rem 8rem  fixed no-repeat,
    darkblue;
}

p {
  color: white;
  font-family: sans-serif;
  font-size: 20px;
  max-width: 30rem;
  padding: 1rem;
  margin: 1rem;
  border: 1px solid white;
}

.b-cursor { /*no z-index here !!!*/
  position: absolute;
  width: 8rem;
  height: 8rem;
  top:var(--my);
  left:var(--mx);
  margin-left: -4rem;
  margin-top: -4rem;
}

.b-cursor:before{
  content:"";
  position:absolute;
  top:-10px;
  left:-10px;
  right:-10px;
  bottom:-10px;
  background:
    radial-gradient(farthest-side, 
      transparent calc(100% - 18px),rgba(231, 232, 192, 1) calc(100% - 15px),
      rgba(231, 232, 192, 1) calc(100% - 10px),transparent 100%);
  border-radius:50%;
  z-index:999;
}

.b-cursor:after {
  content:"";
  position:absolute;
  top:0;
  left:0;
  width:100%;
  height:100%;
  border-radius: 50%;
  z-index: 998;
  background: white;
  mix-blend-mode: difference;
}

<p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Duis pretium pharetra ipsum, at placerat ante maximus vitae. Duis lacus urna, posuere id dapibus in, semper vitae massa. Quisque at egestas nisl. In ex elit, imperdiet eu interdum a, auctor vitae ante. Pellentesque efficitur imperdiet elementum. Integer at nibh gravida nisl sodales ornare ut quis est. Suspendisse sem odio, congue vitae felis at, tincidunt interdum purus. Morbi vitae efficitur est, non congue ante. Proin vel odio et metus sodales lobortis quis ut justo. Phasellus rhoncus eu urna vitae tristique. Suspendisse potenti. Curabitur quis quam lobortis mi laoreet lacinia. Cras non ultrices eros. Nam sed leo et tortor vestibulum cursus nec eu massa. Suspendisse potenti.</p>

<section class="b-cursor">
</section>
<div class="test">
  <p>ja uh misschien werkt dit wel niet</p>
</div>