* {
  box-sizing: border-box;
}

body {
  width: 372px;
  margin: 0;
  padding: 0;
  font-size: 0;
}

.app-title {
  margin: 0;
  margin-bottom: 5px;
  font-size: 12px;
  font-weight: 400;
  color: rgba(#000, 0.5);
}
.app-header {
  border: solid 1px rgba(#000, 0.3);
  padding: 20px;
  padding-top: 15px;
  background-color: #f3f3f3;
}

.search-input {
  width: 100%;
  border-style: solid;
  border-width: 1px;
  border-color: rgba(#000, 0.3);
  padding: 6px 12px;
  font-size: 16px;
  &:focus {
    outline-width: 0;
    border-color: #36c;
    box-shadow: 0 0 5px 2px #9cf;
  }
}

* {
  box-sizing: border-box;
}

body {
  width: 372px;
  margin: 0;
  padding: 0;
  font-size: 0;
}

.app-header {
  border: solid 1px rgba(#000, 0.3);
  padding: 20px;
  padding-top: 15px;
  background-color: #f3f3f3;
}
.app-title {
  margin: 0;
  margin-bottom: 5px;
  font-size: 12px;
  font-weight: 400;
  color: rgba(#000, 0.5);
}

.search-input {
  width: 100%;
  border-style: solid;
  border-width: 1px;
  border-color: rgba(#000, 0.3);
  padding: 6px 12px;
  font-size: 16px;
  &:focus {
    outline-width: 0;
    border-color: #36c;
    box-shadow: 0 0 5px 2px #9cf;
  }
}

Move .app-title rule below .app-header
Move .app-title rule below .app-header

Since the .app-title is contained within the .app-header, .app-title
ought to be listed below .app-header rather than above it.
