Звучит неплохо для фильтра размытия:
.bottom-content {
padding:10px;
position:relative;
z-index:0;
}
.bottom-content::before {
content:"";
position:absolute;
z-index:-1;
top:0;
left:0;
right:0;
bottom:0;
background:lightblue;
filter:blur(6px);
}
<div class="bottom-content">
Here goes some content Here goes some content Here goes some content Here goes some content Here goes some content Here goes some content Here goes some content Here goes some content Here goes some content
</div>
Как показано ниже, только для границы:
.bottom-content {
padding:10px;
position:relative;
z-index:0;
}
.bottom-content::before {
content:"";
position:absolute;
z-index:-1;
top:0;
left:0;
right:0;
bottom:0;
border:8px solid lightblue;
filter:blur(5px);
}
<div class="bottom-content">
Here goes some content Here goes some content Here goes some content Here goes some content Here goes some content Here goes some content Here goes some content Here goes some content Here goes some content
</div>
И также работает только для одной границы:
.bottom-content {
padding:10px;
position:relative;
z-index:0;
}
.bottom-content::before {
content:"";
position:absolute;
z-index:-1;
top:0;
left:0;
right:0;
bottom:0;
border-bottom:8px solid lightblue;
filter:blur(5px);
}
<div class="bottom-content">
Here goes some content Here goes some content Here goes some content Here goes some content Here goes some content Here goes some content Here goes some content Here goes some content Here goes some content
</div>