Html - How to create a smooth, curved SVG mask for a block's top-right corner?

AlexNikolsky
August 27, 2024
181 views
0 votes
2 Answers

I’m trying to create a block with a smooth, curved cut-out in the top-right corner, similar to the image below:

Currently, my implementation looks like this:

As you can see, the current curve is not as smooth as I’d like it to be – It’s essentially not a curve, but a square with straight angles. Here’s my current code:

body {
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh;
  margin: 0;
  background-color: #f0f0f0;
  font-family: Arial, sans-serif;
}

.curved-block {
  width: 300px;
  background-color: white;
  border-radius: 10px;
  box-shadow: 0 2px 10px rgba(0,0,0,0.1);
  position: relative;
  overflow: hidden;
  padding: 5px;
}

.curved-block::after {
  content: '';
  position: absolute;
  top: 0;
  right: 0;
  width: 40px;
  height: 40px;
  background-color: #f0f0f0;
  mask-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='40' height='40' viewBox='0 0 40 40'%3E%3Cpath d='M0 0 h25 c5 0, 10 0, 13 3 s2 7, 2 12 v25 h-40 z' fill='%23000000'/%3E%3C/svg%3E");
  -webkit-mask-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='40' height='40' viewBox='0 0 40 40'%3E%3Cpath d='M0 0 h25 c5 0, 10 0, 13 3 s2 7, 2 12 v25 h-40 z' fill='%23000000'/%3E%3C/svg%3E");
  mask-size: cover;
  -webkit-mask-size: cover;
}

.icon {
  position: absolute;
  top: 8px;
  right: 8px;
  width: 23px;
  height: 23px;
  display: flex;
  justify-content: center;
  align-items: center;
  font-size: 16px;
  font-weight: bold;
  background-color: #0056b3;
  border-radius: 50%;
  color: white;
  z-index: 2;
}

<div class="curved-block">
  <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit.</p>
  <span class="icon">+</span>
</div>

I’m struggling to achieve a smoother, more natural-looking curve in the SVG mask. How can I modify the SVG path to create a curve that looks more like the one in the desired result image? Thank you in advance for your suggestions.

Answers

I did it here: https://css-shape.com/inverted-radius/

You can easily copy the code and adjust the variables:

.inverted-radius {
  --r: 15px; /* the radius */
  --s: 30px; /* the size of the corner*/
  
  height: 150px;
  margin: 10px;
  background: #3FB8AF;
  border-radius: var(--r);
  --_m:/calc(2*var(--r)) calc(2*var(--r))
    radial-gradient(#000 70%,#0000 72%) no-repeat;
  mask:
    right calc(var(--s) + var(--r)) top var(--_m),
    right calc(var(--s) + var(--r)) var(--_m),
    radial-gradient(var(--s) at 100% 0,#0000 99%,#000 101%) 
     calc(-1*var(--r)) var(--r) no-repeat,
    conic-gradient(at calc(100% - var(--s) - 2*var(--r)) calc(var(--s) + 2*var(--r)),
     #0000 25%,#000 0);
}

<div class="inverted-radius"></div>

Since you’re using uniformly rounded corners you may also combine a CSS clip-path with a SVG "goo" filter.

body {
  font-family: Arial, sans-serif;
  margin: 0;
  background-color: #f0f0f0;
  padding: 3em;
}

:root{
  --icon-space: 2em;
  --drop-shadow: drop-shadow(2px 2px 2px rgba(0, 0, 0, 0.75))
}

.curved-block-outer {
  position: relative;
}

.curved-block {
  background-color: #fff;
  padding: 0.5em 2.5em 0.5em 0.5em;
  clip-path: polygon( 0% 0%, calc(100% - var(--icon-space)) 0%, calc(100% - var(--icon-space)) var(--icon-space), 100% var(--icon-space), 100% 100%, 0% 100%);
}

/* round corners via SVG filter; add drop shadow */
.curved-block-filter {
  filter: url("data:image/svg+xml,<svg xmlns='http://www.w3.org/2000/svg'><filter id='goo'><feGaussianBlur in='SourceGraphic' stdDeviation='7.5' result='blur'/><feColorMatrix in='blur' mode='matrix' values='1 0 0 0 0 0 1 0 0 0 0 0 1 0 0 0 0 0 19 -9' result='goo'/><feComposite in='SourceGraphic' in2='goo' operator='atop'/></filter></svg>#goo") var(--drop-shadow);
}

.icon {
  position: absolute;
  right: 0;
  top: 0;
  z-index: 10;
  width: 1.5em;
  height: 1.5em;
  display: block;
  text-align: center;
  font-size: 1em;
  line-height: 1.6em;
  font-weight: bold;
  background-color: #0056b3;
  border-radius: 50%;
  color: #fff;
  filter: var(--drop-shadow);
}

<div class="curved-block-outer ">
  <span class="icon">+</span>
  <div class="curved-block-filter">
    <div class="curved-block">
      <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit.</p>
    </div>
  </div>
</div>

We’re basically

drawing a polygon with 6 vertices with relative units
apply a SVG filter to round the rendering of this polygon

Unfortunately we need some additional wrapping elements otherwise we can’t apply a drop shadow or the plus-button is also affected by the filters.

Goo filter

You can either reference the filter by inlining a SVG in your HTML

<svg class="flt_svg">
    <filter id="goo">
      <feGaussianBlur in="SourceGraphic" stdDeviation="7.5" result="blur" />
      <feColorMatrix in="blur" mode="matrix" values="1 0 0 0 0  0 1 0 0 0  0 0 1 0 0  0 0 0 19 -9" result="goo" />
      <feComposite in="SourceGraphic" in2="goo" operator="atop" />
    </filter>
</svg>

and apply it in CSS like so:

filter: url("#goo")

or you can encode the SVG to a dataURL and embed it directly in CSS

filter: url("data:image/svg+xml,<svg xmlns='http://www.w3.org/2000/svg'><filter id='goo'><feGaussianBlur in='SourceGraphic' stdDeviation='7.5' result='blur'/><feColorMatrix in='blur' mode='matrix' values='1 0 0 0 0 0 1 0 0 0 0 0 1 0 0 0 0 0 19 -9' result='goo'/><feComposite in='SourceGraphic' in2='goo' operator='atop'/></filter></svg>#goo")

The stdDeviation='7.5' value specifies the border/rounding radius.

Html – How to create a smooth, curved SVG mask for a block's top-right corner?

Answers

Goo filter