How to make image scale to fit window in lightbox gallery?

Question

css

Photos of different sizes have been uploaded to the old gallery. Small ones are nothing, but large ones crawl out of the screen on mobile and even on PC.
Here, for example: https://stvitrum.ru/produkciya/dushevye/
Old site on Umi, there is no regular gallery, everything has to be edited in css/html.

lightbox.css

/* line 6, ../sass/lightbox.sass */

#lightboxOverlay {
    position: absolute;
    top: 0;
    left: 0;
    z-index: 9999;
    background-color: black;
    filter: progid: DXImageTransform.Microsoft.Alpha(Opacity=85);
    opacity: 0.85;
    display: none;
}


/* line 15, ../sass/lightbox.sass */

#lightbox {
    position: fixed;
    left: 0;
    top: 0 !important;
    width: 100%;
    z-index: 10000;
    text-align: center;
    line-height: 0;
    font-family: "lucida grande", tahoma, verdana, arial, sans-serif;
    font-weight: normal;
    height: 100vh;
}


/* line 24, ../sass/lightbox.sass */

#lightbox .lb-container img {
    width:  max-content; 
    height:  max-content; 
    
}

.lb-close img {
    width: 90%;
    height: auto;
}


/* line 27, ../sass/lightbox.sass */

#lightbox a img {
    border: none;
}


/* line 30, ../sass/lightbox.sass */

.lb-outerContainer {
    position: relative;
    background-color: white;
    max-width: 90%!important;
    height: auto!important;
    margin: 0 auto;
    -webkit-border-radius: 4px;
    -moz-border-radius: 4px;
    -ms-border-radius: 4px;
    -o-border-radius: 4px;
    border-radius: 4px;
    max-height: 95%;
}


/* line 38, ../../../../.rvm/gems/ruby-1.9.2-p290/gems/compass-0.12.1/frameworks/compass/stylesheets/compass/utilities/general/_clearfix.scss */

.lb-outerContainer:after {
    content: "";
    display: table;
    clear: both;
}


/* line 39, ../sass/lightbox.sass */

.lb-container {
    padding: 10px;
}


/* line 42, ../sass/lightbox.sass */

.lb-loader {
    position: absolute;
    top: 40%;
    left: 0%;
    height: 25%;
    width: 100%;
    text-align: center;
    line-height: 0;
}


/* line 51, ../sass/lightbox.sass */

.lb-nav {
    position: absolute;
    top: 0;
    left: 0;
    height: 100%;
    width: 100%;
    z-index: 10;
}


/* line 59, ../sass/lightbox.sass */

.lb-container>.nav {
    left: 0;
}


/* line 62, ../sass/lightbox.sass */

.lb-nav a {
    outline: none;
}


/* line 65, ../sass/lightbox.sass */

.lb-prev,
.lb-next {
    width: 49%;
    height: 100%;
    background-image: url("data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7");
    /* Trick IE into showing hover */
    display: block;
}


/* line 72, ../sass/lightbox.sass */

.lb-prev {
    left: 0;
    float: left;
}


/* line 76, ../sass/lightbox.sass */

.lb-next {
    right: 0;
    float: right;
}


/* line 81, ../sass/lightbox.sass */

.lb-prev:hover {
    background: url(../images/prev.png) left 48% no-repeat;
}


/* line 85, ../sass/lightbox.sass */

.lb-next:hover {
    background: url(../images/next.png) right 48% no-repeat;
}


/* line 88, ../sass/lightbox.sass */

.lb-dataContainer {
    margin: 0 auto;
    padding-top: 5px;
    *zoom: 1;
    width: 90%!important;
    -moz-border-radius-bottomleft: 4px;
    -webkit-border-bottom-left-radius: 4px;
    -ms-border-bottom-left-radius: 4px;
    -o-border-bottom-left-radius: 4px;
    border-bottom-left-radius: 4px;
    -moz-border-radius-bottomright: 4px;
    -webkit-border-bottom-right-radius: 4px;
    -ms-border-bottom-right-radius: 4px;
    -o-border-bottom-right-radius: 4px;
    border-bottom-right-radius: 4px;
}


/* line 38, ../../../../.rvm/gems/ruby-1.9.2-p290/gems/compass-0.12.1/frameworks/compass/stylesheets/compass/utilities/general/_clearfix.scss */

.lb-dataContainer:after {
    content: "";
    display: table;
    clear: both;
}


/* line 95, ../sass/lightbox.sass */

.lb-data {
    padding: 0 10px;
    color: #bbbbbb;
}


/* line 98, ../sass/lightbox.sass */

.lb-data .lb-details {
    width: 90%;
    float: left;
    text-align: left;
    line-height: 1.1em;
}


/* line 103, ../sass/lightbox.sass */

.lb-data .lb-caption {
    font-size: 13px;
    font-weight: bold;
    line-height: 1em;
}


/* line 107, ../sass/lightbox.sass */

.lb-data .lb-number {
    display: block;
    clear: left;
    padding-bottom: 1em;
    font-size: 11px;
}


/* line 112, ../sass/lightbox.sass */

.lb-data .lb-close {
    width: 35px;
    float: right;
    padding-bottom: 0.7em;
    outline: none;
}


/* line 117, ../sass/lightbox.sass */

.lb-data .lb-close:hover {
    cursor: pointer;
}