styles.css

*,
*:before,
*:after {
  -webkit-box-sizing: border-box;
  box-sizing: border-box;
}

body {
  background-image: -webkit-linear-gradient(45deg, #e53935, #ef5350);
  background-image: -o-linear-gradient(45deg, #e53935, #ef5350);
  background-image: linear-gradient(45deg, #e53935, #ef5350);
  background-attachment: fixed;
  margin: 50px;
  font-family: "Open Sans", sans-serif;
}

h1 {
  margin-top: 20vh;
  color: #fff;
  font-weight: 300;
  text-align: center;
}

#todos-form {
  -webkit-box-shadow: 0 4px 5px 4px rgba(0, 0, 0, 0.08);
  box-shadow: 0 4px 5px 4px rgba(0, 0, 0, 0.08);
  background-color: #fff;
  margin: 10vh auto;
  max-width: 17rem;
  border-radius: 5px;
}

#todos-title {
  margin: 0;
  color: #666;
  font-size: 14px;
  text-align: center;
  padding: 15px;
  padding-bottom: 0;
}

#todos-ul {
  padding-left: 0;
  list-style-type: none;
  max-height: 35vh;
  overflow-y: auto;
  margin-bottom: 0;
}

li {
  overflow: hidden;
  -webkit-transition: 0.2s background-color;
  -o-transition: 0.2s background-color;
  transition: 0.2s background-color;
}

li:hover {
  background-color: rgba(0, 0, 0, 0.04);
}

label {
  display: -webkit-box;
  display: -ms-flexbox;
  display: flex;
  padding: 15px;
  position: relative;
  -webkit-box-pack: justify;
  -ms-flex-pack: justify;
  justify-content: space-between;
}

input[type="checkbox"] {
  position: absolute;
  opacity: 0;
  z-index: -1;
}

input[type="checkbox"] + span:before {
  content: "";
  border: 2px solid #dadada;
  display: inline-block;
  border-radius: 3px;
  padding: 7px;
  margin-right: 10px;
  vertical-align: middle;
  -webkit-transition: 0.1s border-color;
  -o-transition: 0.1s border-color;
  transition: 0.1s border-color;
}

input[type="checkbox"]:checked + span:after {
  content: "";
  position: absolute;
  height: 5px;
  width: 10px;
  left: 4px;
  margin-top: -1px;
  display: inline-block;
  color: #fff;
  border-left: 2px solid;
  border-bottom: 2px solid;
  -webkit-transform: rotate(-45deg);
  -ms-transform: rotate(-45deg);
  transform: rotate(-45deg);
}

input[type="checkbox"]:checked:hover + .todo-text {
  color: #333;
}

label:hover input[type="checkbox"] + span:before {
  border-color: #f44336;
}

input[type="checkbox"]:checked + .todo-text {
  text-decoration: line-through;
  color: #aaa;
  font-style: italic;
  -webkit-transition: 0.2s color;
  -o-transition: 0.2s color;
  transition: 0.2s color;
}

input[type="checkbox"]:checked:hover + .todo-text {
  color: #999;
}

input[type="checkbox"]:checked + span:before {
  border-color: #f44336;
  background-color: #f44336;
}

input[type="checkbox"]:focus + span:before {
  -webkit-box-shadow: 0 0 3px 0 #f44336;
  box-shadow: 0 0 3px 0 #f44336;
}

input[type="checkbox"]:focus + span:before {
  -webkit-animation-name: checkTodo;
  animation-name: checkTodo;
  -webkit-animation-duration: 0.5s;
  animation-duration: 0.5s;
}

.todo-text {
  position: relative;
  font-size: 14px;
  display: -webkit-box;
  display: -ms-flexbox;
  display: flex;
  -webkit-box-align: center;
  -ms-flex-align: center;
  align-items: center;
  color: #888;
  -webkit-transition: 0.2s color;
  -o-transition: 0.2s color;
  transition: 0.2s color;
  word-break: break-all;
}

label:hover .todo-text {
  color: #444;
}

.remove-todo-btn {
  width: 12px;
  height: 12px;
  padding: 10px;
  display: -webkit-box;
  display: -ms-flexbox;
  display: flex;
  -webkit-box-align: center;
  -ms-flex-align: center;
  align-items: center;
  cursor: pointer;
  background-color: transparent;
  border: none;
  border-radius: 50px;
  -webkit-transition: 0.2s background-color;
  -o-transition: 0.2s background-color;
  transition: 0.2s background-color;
}

.remove-todo-btn:before,
.remove-todo-btn:after {
  content: "";
  position: absolute;
  margin: 0;
  height: 11px;
  width: 1px;
  background-color: #ccc;
  border-radius: 1px;
}

.remove-todo-btn:hover {
  background-color: #f44336;
  border-radius: 50%;
}

.remove-todo-btn:hover:before,
.remove-todo-btn:hover:after {
  background-color: #fff;
}

.remove-todo-btn:before {
  -webkit-transform: rotate(45deg);
  -ms-transform: rotate(45deg);
  transform: rotate(45deg);
}

.remove-todo-btn:after {
  -webkit-transform: rotate(-45deg);
  -ms-transform: rotate(-45deg);
  transform: rotate(-45deg);
}

.remove-todo {
  -webkit-animation-name: removeTodo;
  animation-name: removeTodo;
  -webkit-animation-duration: 0.3s;
  animation-duration: 0.3s;
}

#add-todo {
  display: -webkit-box;
  display: -ms-flexbox;
  display: flex;
  -webkit-box-pack: justify;
  -ms-flex-pack: justify;
  justify-content: space-between;
  position: relative;
}

#add-todo-input {
  width: 100%;
  padding: 15px;
  padding-right: 40px;
  border: 0;
  border-top: 1px solid #d2d9e0;
  outline-color: #56aaff;
  border-bottom-left-radius: 5px;
  border-bottom-right-radius: 5px;
  -webkit-transition: 0.2s all;
  -o-transition: 0.2s all;
  transition: 0.2s all;
}

::-webkit-input-placeholder {
  font-family: "Open Sans", sans-serif;
}
:-ms-input-placeholder {
  font-family: "Open Sans", sans-serif;
}
::-moz-placeholder {
  font-family: "Open Sans", sans-serif;
}
:-moz-placeholder {
  font-family: "Open Sans", sans-serif;
}

#add-todo-btn {
  background-color: transparent;
  position: absolute;
  top: 0;
  bottom: 0;
  right: 0;
  padding: 0 16px;
  border: 0;
  cursor: pointer;
  -webkit-transition: 0.2s all;
  -o-transition: 0.2s all;
  transition: 0.2s all;
}

#add-todo-btn:active {
  -webkit-transform: scale(0.8);
  -ms-transform: scale(0.8);
  transform: scale(0.8);
}

.right-arrow {
  position: relative;
  height: 18px;
  width: 14px;
  display: inline-block;
  vertical-align: middle;
  -webkit-transform: scale(0.8);
  -ms-transform: scale(0.8);
  transform: scale(0.8);
  -webkit-transition: 0.2s margin-right;
  -o-transition: 0.2s margin-right;
  transition: 0.2s margin-right;
}

.right-arrow:before,
.right-arrow:after {
  content: "";
  position: absolute;
  border-color: #d2d9e0;
  -webkit-transition: 0.3s border-color;
  -o-transition: 0.3s border-color;
  transition: 0.3s border-color;
}

.right-arrow:before {
  width: 14px;
  left: 0;
  top: 43%;
  border-bottom-width: 2px;
  border-bottom-style: solid;
}

.right-arrow:after {
  height: 12px;
  width: 12px;
  right: 0;
  top: 15%;
  border-style: solid;
  border-width: 2px 2px 0 0;
  -webkit-transform: rotate(45deg);
  -ms-transform: rotate(45deg);
  transform: rotate(45deg);
}

#add-todo-btn:hover .right-arrow:before,
#add-todo-btn:hover .right-arrow:after {
  border-color: #f44336;
}

#add-todo-btn:hover .right-arrow {
  margin-right: -3px;
}

.new-todo {
  -webkit-animation-name: newTodo;
  animation-name: newTodo;
  -webkit-animation-duration: 0.3s;
  animation-duration: 0.3s;
  -webkit-animation-iteration-count: 1;
  animation-iteration-count: 1;
}

::-webkit-scrollbar {
  width: 5px;
}

::-webkit-scrollbar-track {
  background: #f1f1f1;
}

::-webkit-scrollbar-thumb {
  background: #bbb;
}

::-webkit-scrollbar-thumb:hover {
  background: #888;
}

@-webkit-keyframes newTodo {
  0% {
    opacity: 0;
    height: 0;
  }
  100% {
    opacity: 1;
    height: 50px;
  }
}

@keyframes newTodo {
  0% {
    opacity: 0;
    height: 0;
  }
  100% {
    opacity: 1;
    height: 50px;
  }
}

@-webkit-keyframes removeTodo {
  0% {
    height: 50px;
    opacity: 1;
  }
  100% {
    height: 0;
    opacity: 0;
  }
}

@keyframes removeTodo {
  0% {
    height: 50px;
    opacity: 1;
  }
  100% {
    height: 0;
    opacity: 0;
  }
}

@-webkit-keyframes checkTodo {
  0% {
    -webkit-transform: scale(1);
    transform: scale(1);
  }
  50% {
    -webkit-transform: scale(0.75);
    transform: scale(0.75);
  }
  100% {
    -webkit-transform: scale(1);
    transform: scale(1);
  }
}

@keyframes checkTodo {
  0% {
    -webkit-transform: scale(1);
    transform: scale(1);
  }
  50% {
    -webkit-transform: scale(0.75);
    transform: scale(0.75);
  }
  100% {
    -webkit-transform: scale(1);
    transform: scale(1);
  }
}