body {
    background-image: linear-gradient(-45deg, #2177b8 0%, #c35691 50%, #2177b8 100%);
    background-size: 300% 300%;
}

.container {
    display: flex;
    flex-wrap: wrap;
    justify-content: center;
}

.col-1 {
    width: 400px;
    max-width: 99%;
    margin: 0 14px;
    align-self: center;
}

.col-2 {
    width: 500px;
    max-width: 99%;
    margin: 0 14px;
}

.col-3 {
    width: 350px;
    max-width: 99%;
    height: 600px;
    margin: 0 14px;
    margin-top: 20px;
    border-radius: 10px; 
    padding: 10px;
    background-color: rgba(255, 228, 196, 0.7);
    overflow-y: scroll;
}

/* start col-1 */
.current {
    width: 100%;
    height: 100px;
    line-height: 100px;
    border-radius: 10px;
    background-color: rgb(254,167,141);
}
.current-text {
    text-align: center;
    font-size: 23px;
    font-weight: 300;
}

.category {
    display: flex;
    flex-wrap: wrap;
    margin-top: 20px;
}
.change {
    width: 80px;
    height: 50px;
    line-height: 50px;
    border-radius: 10px;
    cursor: pointer;
    box-sizing: border-box;
    text-align: center;
    color: #fff;
    margin-right: 15px;
    margin-top: 15px;
}
.junior { 
    background-color: #de283b;
}
.senior {
    background-color: #ff6366;
}
.cet4 {
    background-color: #FFD700;
}
.cet6 {
    background-color: #00E5FF;
}
.postgraduate {
    background-color: #c69fff;
}
.toefl {
    background-color: #ff8e8c;
}
.sat {
    background-color: #86efac;
}
/* end col-1 */

/* start col-2 */
.word {
    width: 100%;
    height: 300px;
    background-color:rgba(255,228,196,0.7);
    border-radius: 20px;
    display: flex;
    justify-content: center;
    align-items: center;
    text-align: center;
}
#word-title {
    font-size: 50px;
    margin: 0;
}
#word-sense {
    font-size: 20px;
    margin: 15px 7px;
}

.btns {
    width: 100%;
}
.switch-btn {
    width: 46%;
    height: 80px;
    border: 0;
    border-radius: 10px;
    font-size: 2rem;
    color: rgba(0,0,0,0.7);
    cursor: pointer;
}
.left {
    float: left; 
    background-color:rgb(250,143,113);
}
.left:hover {
    background-color:rgba(250,143,113,0.7);
}
.right {
    float: right;
    background-color:rgb(129,214,207);
}
.right:hover {
    background-color: rgba(129,214,207,0.7);
}
.unfamiliar-btn {
    width: 100%;
    height: 100px;
    border: 0;
    border-radius: 10px;
    font-size: 2rem;
    color: rgba(0, 0, 0, 0.7);
    background-color:rgb(248,232,174);
    margin-top: 20px;
    cursor: pointer;
}
/* end col-2 */

/* start col-3 */
.col-3-title {
    text-align: center;
    color: #333;
}
.remove {
    width: 40px;
    height: 20px;
    margin-left: 6px;
    border: 0;
    border-radius: 5px;
    background-color:rgb(230,206,230);
    cursor: pointer;
}
/* end col-3 */