antd-mobile/es/components/side-bar/side-bar.css

<div align="center">

.adm-side-bar {
  --height: 100%;
  --width: 105px;
  --item-border-radius: 8px;
  --background-color: var(--adm-color-fill-content);
  width: var(--width);
  height: var(--height);
  box-sizing: border-box;
  font-size: var(--adm-font-size-main);
  overflow-y: auto;
  transform: translateZ(0);
  -webkit-transform: translateZ(0);
  background-color: var(--background-color);
  display: flex;
  flex-direction: column;
}
.adm-side-bar-items {
  flex: none;
  overflow: hidden;
}
.adm-side-bar-extra-space {
  flex: auto;
  overflow: hidden;
  position: relative;
}
.adm-side-bar-item {
  display: flex;
  align-items: center;
  box-sizing: border-box;
  padding: 16px 12px;
  position: relative;
  cursor: pointer;
  background-color: var(--background-color);
  overflow: visible;
}
.adm-side-bar-item-highlight {
  position: absolute;
  height: 100%;
  width: 2px;
  left: -12px;
  top: 0;
  background: var(--adm-color-primary);
  border-radius: 2px;
}
.adm-side-bar-item-active {
  color: var(--adm-color-primary);
  background-color: var(--adm-color-background);
  position: relative;
}
.adm-side-bar-item-corner {
  width: var(--item-border-radius);
  height: var(--item-border-radius);
  position: absolute;
  z-index: 100;
  right: 0;
  -webkit-user-select: none;
          user-select: none;
  pointer-events: none;
}
.adm-side-bar-item-corner-top {
  top: 0;
  transform: rotate(-90deg);
}
.adm-side-bar-item-corner-bottom {
  bottom: 0;
}
.adm-side-bar-item-disabled {
  cursor: not-allowed;
}
.adm-side-bar-item-disabled .adm-side-bar-item-title {
  opacity: 0.4;
}
.adm-side-bar-badge.adm-badge {
  --right: -4px;
}