Hi Saguaros,
does that mean that this template uses an older version of Bootstrap? Which version of Bootstrap is used on this template?
Anyway, there is a problem with your code: the button remains displayed after clicking on it and when the mouse cursor is not over it.
Here is the corrected version.
.carousel-control-prev,
.carousel-control-next {
opacity: 0 !important;
transition: opacity 0.3s ease-in-out;
position: absolute;
top: 52%;
width: 25px;
height: 25px;
margin-top: -20px;
font-size: 35px;
font-weight: 100;
line-height: 18px;
color: #fff;
text-align: center;
background: rgba(0,0,0,.5);
border: 2px solid #fff;
-webkit-border-radius: 23px;
-moz-border-radius: 23px;
border-radius: 23px;
}
.carousel-control-prev {
left: 15px;
}
.carousel-control-next {
right: 15px;
}
#solidres .carousel:hover > .carousel-control-prev,
#solidres .carousel:hover > .carousel-control-next {
opacity: 1 !important;
}
.carousel-control-prev:focus,
.carousel-control-next:focus,
.carousel-control-prev:active,
.carousel-control-next:active {
opacity: 0 !important;
}
#solidres .carousel:not(:hover) .carousel-control-prev,
#solidres .carousel:not(:hover) .carousel-control-next {
opacity: 0 !important;
}