Hello Roman,
Please change to your color code you prefer with the CSS below with #e9360d which is the red color in your like and paste it in your custom CSS file.
#discuss-wrapper .discuss-likes .btn-likes {
background-color: #e9360d;
background-image: -moz-linear-gradient(top,#e9360d,#e9360d);
background-image: -webkit-gradient(linear,0 0,0 100%,from(#e9360d),to(#e9360d));
background-image: -webkit-linear-gradient(top,#e9360d,#e9360d);
background-image: -o-linear-gradient(top,#e9360d,#e9360d);
background-image: linear-gradient(to bottom,#e9360d,#e9360d);
filter: progid:DXImageTransform.Microsoft.gradient(startColorstr='#ffe9360d', endColorstr='#ffe9360d', GradientType=0);
border-color: #e9360d #e9360d #a12509;
border-color: rgba(0,0,0,0.1) rgba(0,0,0,0.1) rgba(0,0,0,0.25);
border-color: #C00;
border-bottom-color: #900;
}
Hope
Thanks