Faded border loading spinner in CSS - css

Question

How can I make the last part of the spinner lighter (ie. fading):
#loader-wrapper {
position: fixed;
top: 0;
left: 0;
width: 100%;
height: 100%;
z-index: 1000;
}
#loader {
display: block;
position: relative;
left: 50%;
top: 50%;
width: 150px;
height: 150px;
margin: -75px 0 0 -75px;
border-radius: 50%;
border: 5px solid transparent;
border-top-color: #aaa;
border-right-color: #aaa;
animation: spin 2s linear infinite;
}
#keyframes spin {
0% {
transform: rotate(0deg);
}
100% {
transform: rotate(360deg);
}
}
<div id="loader-wrapper">
<div id="loader"></div>
</div>
I tried using gradient but it converts it to a square

Answer 1

You can apply the gradient to a pseudo-element like so:
#loader-wrapper {
position: fixed;
top: 0;
left: 0;
width: 100%;
height: 100%;
z-index: 1000;
}
#loader {
display: block;
position: relative;
left: 50%;
top: 50%;
width: 150px;
height: 150px;
margin: -75px 0 0 -75px;
border-radius: 50%;
border: 5px solid transparent;
border-top-color: #aaa;
border-right-color: #aaa;
animation: spin 2s linear infinite;
}
#loader::after {
content: '';
width: 85%;
height: 85%;
background: linear-gradient(45deg, rgba(255, 255, 255, 1) 0%, rgba(255, 255, 255, 1) 40%, rgba(255, 255, 255, 0.7) 60%, rgba(255, 255, 255, 0) 100%);
position: absolute;
top: 0;
left: 0;
transform: translate(-5%, -5%);
}
#keyframes spin {
0% {
transform: rotate(0deg);
}
100% {
transform: rotate(360deg);
}
}
<div id="loader-wrapper">
<div id="loader"></div>
</div>

Answer 2

Here is another idea with less code and without using pseudo element.
.loader {
--border-width: 5px;
height: 150px;
width: 150px;
border-radius: 50%;
/* 0.5px's are needed to avoid hard-stopping */
--mask: radial-gradient(
farthest-side,
transparent calc(100% - var(--border-width) - 0.5px),
#000 calc(100% - var(--border-width) + 0.5px)
);
-webkit-mask: var(--mask);
mask: var(--mask);
background: linear-gradient(#aaa 30%, transparent 80%) 0 0/50% 100% no-repeat; /* this is our border image */
animation: spin 2s linear infinite;
}
#keyframes spin {
0% {
transform: rotate(0deg);
}
100% {
transform: rotate(360deg);
}
}
<div class="loader"></div>
And this is the comparison of my answer with #Ricky's answer by setting background to body:
#Ricky's way:
body {
background: pink; /* just added this */
}
#loader-wrapper {
position: fixed;
top: 0;
left: 0;
width: 100%;
height: 100%;
z-index: 1000;
}
#loader {
display: block;
position: relative;
left: 50%;
top: 50%;
width: 150px;
height: 150px;
margin: -75px 0 0 -75px;
border-radius: 50%;
border: 5px solid transparent;
border-top-color: #aaa;
border-right-color: #aaa;
animation: spin 2s linear infinite;
}
#loader::after {
content: '';
width: 85%;
height: 85%;
background: linear-gradient(45deg, rgba(255, 255, 255, 1) 0%, rgba(255, 255, 255, 1) 40%, rgba(255, 255, 255, 0.7) 60%, rgba(255, 255, 255, 0) 100%);
position: absolute;
top: 0;
left: 0;
transform: translate(-5%, -5%);
}
#keyframes spin {
0% {
transform: rotate(0deg);
}
100% {
transform: rotate(360deg);
}
}
<div id="loader-wrapper">
<div id="loader"></div>
</div>
My way:
body {
background: pink; /* just added this */
}
.loader {
--border-width: 5px;
height: 150px;
width: 150px;
border-radius: 50%;
/* 0.5px's are needed to avoid hard-stopping */
--mask: radial-gradient(
farthest-side,
transparent calc(100% - var(--border-width) - 0.5px),
#000 calc(100% - var(--border-width) + 0.5px)
);
-webkit-mask: var(--mask);
mask: var(--mask);
background: linear-gradient(#aaa 30%, transparent 80%) 0 0/50% 100% no-repeat; /* this is our border image */
animation: spin 2s linear infinite;
}
#keyframes spin {
0% {
transform: rotate(0deg);
}
100% {
transform: rotate(360deg);
}
}
<div class="loader"></div>