style.css

button {
  height: 50px;
  margin-bottom: 10px;
  margin-right: 10px;
  float: right;
  width: 50px;
  color: #fff;
  text-transform: uppercase;
  background: #484f4f;
  border-radius: 50px;
  display: inline-block;
  border: none;
  font-weight: bold;
  font-size: 20px;
}
button:hover {
  text-shadow: 0px 0px 6px rgba(255, 255, 255, 1);
  -webkit-box-shadow: 0px 5px 40px -10px rgba(0, 0, 0, 0.57);
  -moz-box-shadow: 0px 5px 40px -10px rgba(0, 0, 0, 0.57);
  transition: all 0.4s ease 0s;
}
.sort {
  height: 70px;
  margin-bottom: 10px;
  width: 200px;
  color: #fff !important;
  text-transform: uppercase;
  background: #484f4f;
  display: inline-block;
  border: none;
  font-weight: bold;
  font-size: 20px;
  margin-top: 12px;
}

header {
  background-image: url("https://previews.123rf.com/images/tortoon/tortoon1611/tortoon161100090/65878421-business-concept-top-view-notebook-writing-2017-to-do-list-pen-coffee-cup-and-phone-on-wood-table-.jpg");
  height: 350px;
  background-size: cover;
  background-repeat: no-repeat;
  
}
html {
  background-color: #f0efef;
  border: 2px solid gray;
  box-shadow: 0px 0px 3px 3px #bf8040;
  margin: 10px;
  padding: 10px;
}
li {
  margin-bottom: 40px;
}
form {
  margin-top: 10px;
  margin-left: 25%;
}


label{
  font-size: 20px;
}
.todo {
  width: 300px;
  height: 50px;
  padding-left: 10px;
}
.add {
  width: 100px;
  height: 56px;
  font-size: 25px;
  border-radius: 5px;
  margin-top: 1%;
 float: none; 
}

span {
  width: 200px;
  font-size: 25px;
  font-weight: bold;
}

div {
  box-sizing: inherit;

  width: 49%;
  display: inline-block;
  border: 2px solid black;
  height: 500px;
}

.markTodocontainer {
  float: right;
  background-color: #b1cbbb;
}
.todocontainer {
  background-color: #deeaee;
  
}

.head {
  text-decoration: underline;
  -webkit-text-decoration-color: #ccccb3; 
  text-decoration-color: #ccccb3;
  font-size: 50px;
  margin: 2%;
  width: 45%;
  color: #484f4f;
  display: inline-block;
  text-shadow: 2px 2px 8px #92a8d1;
  margin-top: 57px;
  margin-bottom: 18px;
}
.sort-buttons {
  margin-top: 10px;
  margin-left: 25%;
  width: auto;
  height: auto;
  border: none;
}