Glowing border animation with CSS doesn't have a fluid transition - html

Question

I'm following a tutorial on youtube on how to create a Glowing Border Animation with CSS
I tried to implement it myself and was pretty successful, however, I encountered a problem which I'm unable to solve. When I view my animation there is an uneven transition. It looks like as if two images are stuck together where the colours transition is cut off.
How can I solve the issue there with my transition looks smooth?
I created a JSFiddle to display what I mean:
* {
margin: 0;
padding: 0;
}
body {
height: 100vh;
display: flex;
align-items: center;
justify-content: center;
background: #151320;
}
.box {
position: relative;
width: 300px;
height: 300px;
color: #fff;
font: 300 2rem 'Montserrat';
text-align: center;
text-transform: uppercase;
display: flex;
align-items: center;
}
.box::before,
.box::after {
content: '';
z-index: -1;
position: absolute;
width: calc(100% + 30px);
height: calc(100% + 30px);
top: -15px;
left: -15px;
background: linear-gradient(45deg, #0096FF, #0047AB, #000000, #6082B6, #87CEEB, #00008B, #145DA0, #00008B, #145DA0, #0096FF, #0047AB, #000000, #6082B6, #87CEEB);
background-repeat: repeat;
border-radius: 5px;
background-size: 600%;
animation: border 12s linear infinite;
}
.box::after {
filter: blur(25px);
}
#keyframes border {
0% {
background-position: 0% 0%;
}
100% {
background-position: 250% 250%;
}
}
<link href='https://fonts.googleapis.com/css?family=Montserrat' rel='stylesheet'>
<div class="box">
Greetings fellow developer!
</div>
Note: The animation looks smooth at first but after about 7ish seconds you encounter the "cut off" where the transition doesn't line up.

Answer 1

Your gradient need to have a kind of repetition to achieve such effect. Make its size 200% 200% then use a repeating gradient where the first color start at 0% and the last one at 50%. Notice how the list of color is repeated twice but in the opposite order.
body {
background: #151320;
}
.box {
position: relative;
width: 300px;
height: 300px;
}
.box::before,
.box::after {
content: '';
z-index: -1;
position: absolute;
inset: -15px;
background:
repeating-linear-gradient(45deg,
#0096FF 0%, #0047AB, #6082B6, #87CEEB, #00008B,
#00008B, #87CEEB, #6082B6,#0047AB,#0096FF 50%);
border-radius: 5px;
background-size: 200% 200%;
animation: border 2s linear infinite;
}
.box::after {
filter: blur(25px);
}
#keyframes border {
0% {
background-position: bottom left;
}
100% {
background-position: top right;
}
}
<div class="box">
</div>