在背景上带有透明边框的圆圈

Question

我怎样才能在 CSS 中实现这样的事情？

我已经尝试了很多方法，但深色背景仍然挡住了并且无法剪裁，因此它下面的背景图像不可见......

.item {
  position: relative;
}
    
.item:before {
  content: '';
  size(100%);
  top: 0;
  left: 0;
  z-index: 1;
  background: rgba(0, 0, 0,0 0.1);
}

<div class="item">
   <img>
   <span class="rate">
     <span class="amount">10</span> ??????
   </span>
</div>  

我正在寻找一种能够使部分深色背景透明的方法，以便可以看到图像。

Answer 1

这可以使用径向渐变来实现，（示例拆分为单独的行以使其更易于阅读）

background-image: radial-gradient(
   /* Position the circle at the center, 40px from the top */
  circle at center 40px,
  /* The center of the radius should be dark */
  rgba(0,0,0,0.4) 0%,
  /* This is the inner edge of the circle, we transition from dark-transparent between pixels 30 and 31 */
  rgba(0,0,0,0.4) 30px, rgba(0,0,0,0) 31px, 
  /* This is the outer edge of the circle, we transition back from transprent-dark between pixels 34 and 35*/
  rgba(0,0,0,0) 34px, rgba(0,0,0,0.4) 35px,  
  /* Everything outside of the circle should be dark */
  rgba(0,0,0,0.4) 100%
);

哪里circle at center 40px定义了圆相对于父元素的位置（水平居中，从顶部向下 40 像素）记住这是圆心的位置，所以你需要考虑它的半径。

我们在渐变之间使用非常小的步长，使它看起来像一条实线而不是模糊的渐变（我发现1px差异有助于防止线上出现锯齿并使一切看起来更平滑）

可以调整圆的大小或者通过改变所述线的厚度30px，31px，34px和35px在梯度值。

工作示例：

background-image: radial-gradient(
   /* Position the circle at the center, 40px from the top */
  circle at center 40px,
  /* The center of the radius should be dark */
  rgba(0,0,0,0.4) 0%,
  /* This is the inner edge of the circle, we transition from dark-transparent between pixels 30 and 31 */
  rgba(0,0,0,0.4) 30px, rgba(0,0,0,0) 31px, 
  /* This is the outer edge of the circle, we transition back from transprent-dark between pixels 34 and 35*/
  rgba(0,0,0,0) 34px, rgba(0,0,0,0.4) 35px,  
  /* Everything outside of the circle should be dark */
  rgba(0,0,0,0.4) 100%
);

.item {
  position: relative;
  width: 200px;
  height: 200px;
  background: url(https://picsum.photos/seed/picsum/200/200);
}

.item:before {
  position: absolute;
  content: '';
  top: 0;
  left: 0;
  bottom: 0;
  right: 0;
  z-index: 1;
  /* This is the ring itself, you can adjust it's size using the pixel values, leaving 1px differnce usually leaves the best result for smooth edges */
  background-image: radial-gradient(circle at center 40px, rgba(0, 0, 0, 0.4) 0%, rgba(0, 0, 0, 0.4) 30px, rgba(0, 0, 0, 0) 31px, rgba(0, 0, 0, 0) 34px, rgba(0, 0, 0, 0.4) 35px, rgba(0, 0, 0, 0.4) 100%);
}

（此方法与几乎所有自 2010 年以来发布的浏览器兼容）

Answer 2

Infinite box-shadowwithoverflow: hidden;我不知道它是否适合你，我只是试过-

<style>
  .item img {
    max-width: 100%;
    vertical-align: top;
  }

  .item {
    font-family: 'Amiri', serif;
    width: 300px;
    margin: 20px auto;
    overflow: hidden; /* STEP-1 */
    position: relative;
  }

  .rate {
    position: absolute;
    width: 100px;
    height: 100px;

    border-radius: 100%;
    background: rgba(0,0,0,.7);
    top: 80px;
    left: 50%;
    transform: translatex(-50%);
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    font-size: 22px;
    color: #fff;
  }

  .rate::before {
    position: absolute;
    content: '';
    width: calc(100% + 10px);
    height: calc(100% + 10px);
    top: -5px;
    left: 50%;
    transform: translatex(-50%);
    border-radius: 100%;
    box-shadow: 0 0 0 100vh rgba(0,0,0,.7); /* STEP-2 */
  }

  .amount {
    font-size: 20px;
    font-weight: 700;
    display: block;
  }
</style>



<link href="https://fonts.googleapis.com/css2?family=Amiri:wght@400;700&display=swap" rel="stylesheet">

<div class="item">
   <img src="https://images.pexels.com/photos/4888690/pexels-photo-4888690.jpeg?auto=compress&cs=tinysrgb&dpr=2&h=650&w=940" alt="Card title">
   <span class="rate">
     <span class="amount">??</span> ??????
   </span>
</div>