.all_content{
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    margin:1em;
}

.ct_bx{
    display: flex;
    flex-direction: column;
    justify-content: start;
    align-items: center;
}

.ct{
    margin-top:1.5em;
    margin-bottom:0.5em;
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
}

#motivation{
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    margin:1em;
    padding:0.5em;
}

#motivation p{
    /*text-indent: 2em;*/
    text-align: justify;
}

#refereces{
    margin:1em;
}

#references ul{
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;

}

#references ul li{
    /*no bullet*/
    list-style-type: none;
    margin-bottom:1em;
    padding:0.5em;
}

#references ul li a{
    color: black;
}

.ct_pipe{
    display: flex;
    flex-direction: row;
    justify-content: space-evenly;
    align-items: center;
    margin:1em;
    /*background: black;
    color: white;*/
}

.ct_layer{
    display: flex;
    flex-direction: row;
    align-items: center;
    flex: 1;
    height: 100%;
}

.ct_content{
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    height: 100%;
}

.ct_item{
    margin:0.5em;
    padding:0.5em;
    height: 10em;
}

.ct_item h4{
    background: black;
    color: white;
    font-size: 1.2em;
    border-radius: 0.5em;
    text-align: center;
}

/*colorful ct_item*/
.ct_layer:nth-child(1) .ct_item h4{
    /*blue*/
    background: #87CEEB;
    color: black;
}


.ct_layer:nth-child(3) .ct_item h4{
    background: #ffe656;
    color: black;
}

.ct_layer:nth-child(5) .ct_item h4{
    background: #ff79bc;
    color: black;
}

/*add arrow*/
.ct_arrow{
    content: '';
    display: block;
    width: 0;
    height: 0;
    border-top: 0.5em solid transparent;
    border-bottom: 0.5em solid transparent;
    border-left: 0.5em solid black;
    margin: 0.5em;
}

/*RWD*/
@media screen and (max-width: 1024px){
    .ct_pipe{
        flex-direction: column;
    }

    .ct_layer{
        flex-direction: column;
    }

    .ct_item{
        height: fit-content;
    }

    .ct_arrow{
        content: '';
        display: block;
        width: 0;
        height: 0;
        border-left: 0.5em solid transparent;
        border-right: 0.5em solid transparent;
        border-top: 0.5em solid black;
        margin: 0.25em;
    }
}