*,
*::before,
*::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

:root {
  --dark-grey: #1b1b32;
  --light-grey: #f5f6f7;
  --golden-yellow: #fecc4c;
  --yellow: #ffcc4c;
  --gold: #feac32;
  --orange: #ffac33;
  --dark-orange: #f89808;
  --border: 0.2rem solid darkgrey;
  --padding: 0.3rem;
}

body {
  padding: 5px;
  background-color: var(--dark-grey);
  color: var(--light-grey);
  font-family: 'Lato', Helvetica, Arial, sans-serif;
  font-size: 20px;
}

h1 {
  margin: 5rem auto 2rem;
  text-align: center;
}

p {
  padding: var(--padding);
}

#regex-container {
  display: flex;
  align-items: center;
  justify-content: center;
  max-width: 680px;
  margin: 20px auto;
  border: var(--border);
}

#regex-container > label {
  flex: 1 1 auto;
  padding: var(--padding);
}

#pattern-container {
  display: inline-block;
  margin: 5px;
  border: var(--border);
  background-color: var(--light-grey);
  color: var(--dark-grey);
}

#pattern {
  width: calc(100% - 1.2rem);
  margin: 0.2rem;
  border: 0;
  font-size: 1rem;
}

#pattern:focus {
  outline: none;
}

#flags-container {
  display: flex;
  flex: 1 1 auto;
  align-items: center;
}

#flags-container > label {
  margin-right: 0.3rem;
  padding: var(--padding);
}

#test-container {
  display: flex;
  flex: 0 0 auto;
  flex-direction: column;
  max-width: 680px;
  margin: 20px auto;
  border: var(--border);
}

#test-string {
  min-height: 5rem;
  padding: 0.5rem;
  border: 0;
  border-top: var(--border);
  background-color: var(--light-grey);
  color: var(--dark-grey);
  font-size: 1.2rem;
  resize: vertical;
}

::placeholder {
  color: var(--dark-grey);
}

.btn {
  display: block;
  width: 8rem;
  margin: 0.2rem auto;
  cursor: pointer;
  border: 0.2rem solid var(--gold);
  background-color: var(--gold);
  background-image: linear-gradient(var(--golden-yellow), var(--orange));
  color: var(--dark-grey);
  font-size: 1.1rem;
}

.btn:hover {
  background-image: linear-gradient(var(--yellow), var(--dark-orange));
}

#result-container {
  display: flex;
  align-items: center;
  justify-content: center;
  max-width: 680px;
  margin: 20px auto;
}

h2 {
  flex: 0 1 auto;
  align-self: flex-start;
  margin: 0.4rem 0.2rem 0.2rem;
}

#result {
  flex: 1 1 auto;
  min-height: 3rem;
  margin: 0.2rem;
  border: var(--border);
  background-color: var(--light-grey);
  color: var(--dark-grey);
  font-size: 1.5rem;
}

.highlight {
  background-color: lightgreen;
}