el-input-number 属性 controls-position 值为 right 时；

<el-input-number v-model="num" controls-position="right" :min="1" :max="10"></el-input-number>

原生效果

修改后效果

CSS 修改

.el-input-number {
    .el-input-number__increase {// 上 按钮
        top: 2px;
        .el-icon-arrow-up:before {// 三角形
            content: '';
            display: inline-block;
            height: 0;
            width: 0;
            border-style: solid;
            border-width: 6px 4px 6px 4px;
            border-color: rgba(0,0,0,0) rgba(0,0,0,0) #999999 rgba(0,0,0,0);
            transform: translateY(-3px);
        }
    }
    .el-input-number__decrease {//下 按钮
        bottom: 2px;
        .el-icon-arrow-down:before {// 三角形
            content: '';
            display: inline-block;
            height: 0;
            width: 0;
            border-style: solid;
            border-width: 6px 4px 6px 4px;
            border-color: #999999 rgba(0,0,0,0) rgba(0,0,0,0) rgba(0,0,0,0);
            transform: translateY(3px);
        }
    }
}