.boxflex_image img {
    display: block;
    max-width: 100%;
}

.boxflex_text {
    box-sizing: border-box;
}

@media screen and (max-width: 767.98px) {
    .boxflex_text {
        padding: 60px 20px;
    }
}
@media screen and (min-width: 768px) {
    .boxflex {
        position: relative;
    }
    .boxflex_text {
        padding: 60px;
    }
}
@media screen and (min-width: 768px) and (max-width: 1100px) {
    .boxflex_text {
        position: absolute;
        top: 50%;
        left: 50%;
        transform: translateX(-50%) translateY(-50%);
        width: 80%;
        background-color: rgba(255, 255, 255, 0.9);
    }
}
@media screen and (min-width: 1100px) {
    .boxflex_text {
        border: 1px solid #000;
        background-color: #fff;
    }
    .boxflex_image {
        position: relative;
        top: 0px;
        left: 50%;
        transform: translateX(-100%);
        width: 50%;
        max-width: 700px;
    }
    .boxflex_text {
        position: absolute;
        top: 50%;
        left: 45%;
        transform: translateY(-50%);
        width: 50%;
        max-width: 700px;
    }
    .box:nth-of-type(even) .boxflex_image {
        transform: translateX(0%);
    }
    .box:nth-of-type(even) .boxflex_text {
        left: 55%;
        transform: translateX(-100%) translateY(-50%);
    }
}

    ul {
        max-width: 960px;
    }
 
    ul li {
        display: flex;
        align-items: center;
    }
 
 
    ul li .photo,
    ul li .txt {
        width: 50%;
        box-sizing: border-box;
    }

    /* 奇数の行に対して指定 */
    ul li:nth-child(odd) {
        flex-direction: row-reverse;
    }
 
 
    /* 必要に応じて余白つけてください */
    ul li:nth-child(odd) .txt {
        padding-right: 10px;
    }
 
    ul li:nth-child(even) .txt {
        padding-left: 10px;
    }