style.css

@import url(//fonts.googleapis.com/earlyaccess/notosanskr.css);

.notosanskr * { 
 font-family: 'Noto Sans KR', sans-serif;
}

body{
    margin : 0;
    font-family: 'Noto Sans KR', sans-serif;

}

h1{
    font-weight: 800;
}

.container{
    background-color: white;
    min-height: 100vh;
    width: 50rem;
    border: 5px solid black;
    border-radius:30px
}

.task-tabs{
    display: flex;
    border-bottom: 1px solid lightgray;
    position: relative;
    font-weight: 600;
}

.task-tabs div{
    padding:1em;
}

.task-area{
    border: 1px solid lightgray;
}

#under-line{
    height : 4px;
    background-color: black;
    position: absolute;
    left: 0px;
    width: 52px;
    top: 56px;
    padding : 0px;
    transition:0.5s
}

.task{
    display: flex;
    justify-content: space-between;
    padding : 1em;
}

.task-done{
    text-decoration: line-through;
}

.check-button{
    color: black;
    background-color: white;
    border : none;
}

.check-button2{
    color: black;
    background-color: white;
    border : none;
}

.delete-button{
    color: black;
    background-color: white;
    border : none;
}

.task-tabs div{
    cursor:pointer;
}

#task-input{
    border: 3px solid black;
    border-radius: 5px;
}

#add-button{
    background-color: black;
    color : white;
    border-radius: 5px;
    font-weight: 600;
}