Custom css in prebought wordpress theme - Hemma

Hello. I cannot make my logo to be responsive in a theme “Hemma” I bought. So when I open my website on a phone the logo is to wide. Please see www.hotelldahlstromskagarden.se.

I contacted the author but he said that you had to change the theme file… Can any of you see how that can be made?

/*--------------------------------------------------------------

Header

--------------------------------------------------------------*/
.site-header {
position: absolute;
top: 0;
left: 0;
right: 0;
z-index: 9;
height: 90px;
padding: 15px 0px;
font-size: 0.875rem;
font-weight: 700;
letter-spacing: 1px;
color: #333;
background-color: #FFF;
-webkit-box-shadow: 0 0 1px rgba(0, 0, 0, 0.15);
box-shadow: 0 0 1px rgba(0, 0, 0, 0.15);
}

.site-header.is-header-fixed {
-webkit-transition: -webkit-transform .25s;
transition: -webkit-transform .25s;
transition: transform .25s;
transition: transform .25s, -webkit-transform .25s;
}

.site-header .site-branding {
float: left;
}

.site-header .site-title {
margin-bottom: 0;
text-transform: uppercase;
}

.site-header .site-title a {
display: block;
line-height: 60px;
}

.site-header a {
color: #333;
}

.is-nav-open .site-header {
-webkit-transform: none !important;
-ms-transform: none !important;
transform: none !important;
}

.is-nav-open .site-header a {
color: #333 !important;
}

.site-header .select-language {
line-height: 60px;
text-transform: uppercase;
float: right;
}

.site-header .select-language a {
color: #AEB1B5;
}

.site-header .select-language a:hover {
color: #333;
}

.site-header .select-language a img {
margin-bottom: 0;
}

.site-header .select-language .current-lang a {
color: #333;
}

.site-header.is-hero-on .site-branding a {
color: rgba(255, 255, 255, 0.85);
}

.site-header.is-hero-on .site-branding a:hover {
color: #FFF;
}

@media screen and (min-width: 1020px) {
.is-menu-desktop .site-header.is-hero-on .main-navigation > div > ul > li > a {
color: rgba(255, 255, 255, 0.85);
}
.is-menu-desktop .site-header.is-hero-on .main-navigation > div > ul > li > a:hover {
color: #FFF;
}
}

.site-header.is-hero-on .select-language > ul > li > a {
color: rgba(255, 255, 255, 0.5);
}

.site-header.is-hero-on .select-language > ul > li > a:hover {
color: rgba(255, 255, 255, 0.7);
}

.site-header.is-hero-on .select-language .current-lang > a {
color: #FFF;
}

.site-header.is-hero-on .menu-toggle .nav-icon {
background-color: #FFF;
}

.site-header.is-header-fixed {
position: fixed;
background-color: rgba(255, 255, 255, 0.97);
-webkit-transform: translateY(-100%);
-ms-transform: translateY(-100%);
transform: translateY(-100%);
}

.site-header.is-header-fixed.is-header-transitioning {
-webkit-transition: -webkit-transform .35s;
transition: -webkit-transform .35s;
transition: transform .35s;
transition: transform .35s, -webkit-transform .35s;
}

.site-header.is-header-fixed.is-header-visible {
-webkit-transform: none;
-ms-transform: none;
transform: none;
}

.site-header.is-header-fixed.is-header-hidden {
visibility: hidden;
opacity: 0;
}

.site-header.is-hero-on {
-webkit-box-shadow: none;
box-shadow: none;
background-color: transparent;
}

@media screen and (min-width: 769px) {
.is-block-frame .site-header.is-hero-on {
margin: 20px 0;
}
}

@media screen and (min-width: 769px) {
.is-block-frame .site-header.is-hero-on {
margin-right: 20px;
margin-left: 20px;
}
}

.is-logo-image .site-header .site-branding {
font-size: 0;
}

.is-logo-image .site-header .site-title {
text-indent: -9999px;
height: 60px;
width: 60px;
display: block;
background-repeat: no-repeat;
background-position: center center;
background-size: auto 60px;
}

.is-logo-centered .site-header .site-branding {
position: absolute;
display: inline-block;
left: 50%;
-webkit-transform: translateX(-50%);
-ms-transform: translateX(-50%);
transform: translateX(-50%);
}