<el-input-number size="small" class-unit="%" class="inputNumberClass"></el-input-number>

// css
.inputNumberClass[class-unit] {
    --el-input-number-unit-offset-x: 35px;
    position: relative;
}
.inputNumberClass[class-unit]::after {
    content: attr(class-unit);
    height: 100%;
    display: flex;
    align-items: center;
    position: absolute;
    top: 0;
    right: var(--el-input-number-unit-offset-x);
    color: #999999;
}
.inputNumberClass[class-unit] .el-input__inner {
    padding-left: 30px;
    padding-right: calc(var(--el-input-number-unit-offset-x) + 12px);
}