CSS 데모: scrollbar-gutter
selector {
    scrollbar-gutter: auto | stable |  stable both-edges
}
/* 키워드 값 */
scrollbar-gutter: auto; /* 초깃값 */
scrollbar-gutter: stable;
scrollbar-gutter: stable both-edges; /* scrollbar-gutter: both-edges stable;와 동일함 */

/* 글로벌 값 */
scrollbar-gutter: inherit;
scrollbar-gutter: initial;
scrollbar-gutter: revert;
scrollbar-gutter: revert-layer;
scrollbar-gutter: unset;
<div class="container">
    Lorem Ipsum is simply dummy text of the printing and
    typesetting industry. Lorem Ipsum has been
    the industry's standard dummy text ever since the 1500s,
    when an unknown printer...
</div>
.container {
    width: 250px;
    height: 200px;
    border: 5px solid #663399;
    background: rgba(255, 0, 200, .15);
    overflow: auto;
    scrollbar-gutter: auto; /* 초깃값으로 작성하지 않더라도 scrollbar-gutter: auto;가 적용됨 */
}
.container {
    width: 250px;
    height: 200px;
    border: 5px solid #663399;
    background: rgba(255, 0, 200, .15);
    overflow: auto;
    scrollbar-gutter: auto; /* 초깃값으로 작성하지 않더라도 scrollbar-gutter: auto;가 적용됨 */
}
실제 적용된 모습
<div class="container">
    Lorem Ipsum is simply dummy text of the printing and
    typesetting industry. Lorem Ipsum has been
    the industry's standard dummy text ever since the 1500s,
    when an unknown printer...
</div>
.container {
    width: 250px;
    height: 200px;
    border: 5px solid #663399;
    background: rgba(255, 0, 200, .15);
    overflow: auto;
    scrollbar-gutter: stable;
}
실제 적용된 모습
<div class="container">
    Lorem Ipsum is simply dummy text of the printing and
    typesetting industry. Lorem Ipsum has been
    the industry's standard dummy text ever since the 1500s,
    when an unknown printer...
</div>
.container {
    width: 250px;
    height: 200px;
    border: 5px solid #663399;
    background: rgba(255, 0, 200, .15);
    overflow: auto;
    scrollbar-gutter: stable both-edges;
}
실제 적용된 모습