div 안에 div background-color 질문합니다

.wrap-mouse .mouse-wrap img{
    position: relative;
    right: 130px;
    margin-top: 40px;

    z-index: 1; /* 추가 */
}

 

/* -------------------------- 추가 -------------------------- */
.mouse-wrap {
    position: relative;
}
.wrap-mouse .mouse-wrap .img-shadow {
    position: absolute;
    right: 90%;
    top: 50%;
    width: 1px;
    height: 1px;
    box-shadow: 0 0 8em 8em #43bef9;
}

/* -------------------------- 추가 -------------------------- */

<div class="mouse-wrap">
    <img src="./img/g703.png" alt="">
    <div class="img-shadow"></div> <!-- 추가 -->
</div>