Styling

main.css

body {
  font: 14px "Helvetica Neue", Helvetica, Arial, sans-serif;
  line-height: 14px;
  background: #f5f5f5;
  color: #4d4d4d;
  margin: 1em;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  font-weight: 300;
  display: flex;
  flex-direction: column;
  align-items: center;
  box-sizing: border-box;
}

nav {
  position: relative;
  top: -1em;
  padding: 1em;
  background: rgba(175, 47, 47, 0.2);
  width: 100%;
  height: 3em;
  box-shadow: inset 0 -2px 1px rgba(175, 47, 47, 0.1);
  display: flex;
  justify-content: space-between;
}

.disabled svg {
  fill: gray;
}

header {
  height: 10em;
}

h1 {
  text-align: center;
  font-size: 7em;
  font-weight: 100;
  color: rgba(175, 47, 47, 0.15);
  -webkit-text-rendering: optimizeLegibility;
  -moz-text-rendering: optimizeLegibility;
  text-rendering: optimizeLegibility;
}

main {
  display: flex;
  flex-direction: column;
  align-items: flex-start;
  background: #fff;
  width: 80%;
  box-shadow: 0 2px 4px 0 rgba(0, 0, 0, 0.2), 0 25px 50px 0 rgba(0, 0, 0, 0.1);
  border-radius: 3px;
}

form {
  width: 100%;
  margin: 0;
}

input {
  text-align: center;
  font-size: 1.7em;
  padding: 1em;
  border: none;
  background: rgba(0, 0, 0, 0.005);
  box-shadow: inset 0 -2px 1px rgba(0, 0, 0, 0.03);
  width: 100%;
  outline: none;
}

input::-webkit-input-placeholder {
  font-style: italic;
  font-weight: 300;
  color: #e6e6e6;
}

ul {
  width: 100%;
  margin: 0;
  margin-inline: 0;
  padding-inline: 0;
}

li {
  width: 100%;
  list-style-type: none;
  display: flex;
  align-items: center;
  border-bottom: 1px solid rgba(0, 0, 0, 0.1);
}

.todo {
  padding: 1em;
}

.text {
  font-size: 1.5em;
}

.toggle {
  margin-left: 2em;
  display: flex;
  justify-content: center;
  align-items: center;
  font-weight: 700;
  color: green;
  font-size: 1em;
  width: 0.1em;
  height: 0.1em;
  border: 1px solid lightgray;
  border-radius: 50%;
  cursor: pointer;
}

.delete {
  position: absolute;
  right: 15%;
  cursor: pointer;
  font-weight: 900;
  color: rgba(175, 47, 47, 0.5);
}

.done {
  text-decoration: line-through;
  color: lightgray;
}

.list-manager {
  display: flex;
  justify-content: center;
  padding: 1em 0;
  width: 100%;
}

a {
  font-size: 0.6em;
  text-align: center;
  background: rgba(0, 0, 0, 0.03);
  box-shadow: inset 0 -2px 1px rgba(0, 0, 0, 0.03);
  border: 1px solid lightgray;
  border-radius: 5px;
  outline: none;
  margin: 0 1em;
  padding: 1em;
  min-width: 15%;
  cursor: pointer;
  color: black;
  text-transform: uppercase;
}

a:active {
  box-shadow: none;
  background: rgba(0, 0, 0, 0.01);
}

a:active.selected {
  box-shadow: inset 0 -2px 1px rgba(0, 0, 0, 0.03);
  background: rgba(0, 0, 0, 0.03);
}

.selected {
  color: lightgray;
  cursor: not-allowed;
}