html, body {
  font-family: 'Dosis', sans-serif;
  font-size: 1rem;
  width: 100%;
  box-sizing: border-box;
}

.header {
  position: relative;
  background-color: orange;
  text-align: center;
  width: 100%;
  padding: 10px 0;
  z-index: 10;
  font-size: 2rem;
}

.content {
  margin-top: 5rem;
  text-align: center;
  width: 100%;
}

.input_field {
  width: 300px;
  height: 40px;
  border: 1px black solid;
  outline: none;
  font-family: 'Dosis', sans-serif;
  font-size: 1.2rem;
}

.search_btn {
  cursor: pointer;
  color: white;
  background-color: black;
  border: 1px black solid;
  height: 44px;
  width: 44px;
  outline: none;
}

html, body {
  font-family: 'Dosis', sans-serif;
  font-size: 1rem;
  width: 100%;
  box-sizing: border-box;
}

.header {
  position: relative;
  background-color: orange;
  text-align: center;
  width: 100%;
  padding: 10px 0;
  z-index: 10;
  font-size: 2rem;
}

.content {
  margin-top: 5rem;
  text-align: center;
  width: 100%;
}

.input_field {
  width: 300px;
  height: 40px;
  border: 1px black solid;
  outline: none;
  font-family: 'Dosis', sans-serif;
  font-size: 1.2rem;
  vertical-align: middle;
}

.search_btn {
  cursor: pointer;
  color: white;
  background-color: black;
  border: 1px black solid;
  height: 44px;
  width: 44px;
  outline: none;
  vertical-align: middle;
}

Align the input field and the button
Align the input field and the button
