/* variables for palette shitts and margins (mobile-first) */
:root {
  --color-background: #f4f4f4;    /* background color */
  --color-body-bg: #ffffff;       /* cards' color and footer's color */
  --color-text: #333333;
  --color-primary: #2c3e50;       /* H1 color  */
  --color-secondary: #2980b9;     /* Links and elements color */
  --color-preferred: #4b5ae6;     /* Links and elements color */
  --color-border: #dddddd;
  --color-success: #27ae60;
  --color-error: #e74c3c;

  --font-size-base: 16px;
  --font-size-medium: 20px;
  --font-size-large: 24px;
  --padding-base: 16px;
  --margin-base: 16px;
  --max-width: 960px;
  --max-width-lesson: 500px;
}

/* margins reset and basic style */
* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

body {
  font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif;
  background-color: var(--color-background);
  color: var(--color-text);
  font-size: var(--font-size-base);
  line-height: 1.6;
}

/* center box */
.container {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: var(--padding-base);
}

/* Logo' style and chapters' style */
.logo {
  text-align: center;
  margin: var(--margin-base) 0;
  font-size: var(--font-size-large);
  font-weight: bold;
}

.logo-img {
  max-width: 200px;
  width: 100%;
  height: auto;
}

.chapter-card {
  display: block;
  text-decoration: none;
  background-color: var(--color-body-bg);
  border: 1px solid var(--color-border);
  border-radius: 4px;
  margin-bottom: var(--margin-base);
  overflow: hidden;
  cursor: pointer;
  transition: box-shadow 0.3s ease, transform 0.3s ease;
}

.chapter-card:active {
  transform: scale(0.995);
}

.chapter-card:hover {
  box-shadow: 0 4px 8px rgba(0, 0, 0, 0.1);
}

.chapter-header {
  display: flex;
  align-items: center;
  padding: var(--padding-base);
}

.chapter-number {
  font-size: var(--font-size-large);
  font-weight: 500;
  border-radius: 50%;
  flex-shrink: 0;
  width: 32px;
  height: 32px;
  display: flex;
  align-items: center;
  justify-content: center;
  margin-right: var(--margin-base);
  color: var(--color-text);
  text-align: center;
}

.chapter-title {
  font-size: var(--font-size-medium);
  color: var(--color-primary);
}


.chapter-lessons-preps {
  display: none;
  border-top: 1px solid var(--color-border);
}

.chapter-lessons-articles {
  display: none;
  border-top: 1px solid var(--color-border);
}

.chapter-lessons-preps a {
  display: block;
  padding: var(--padding-base);
  text-decoration: none;
  color: var(--color-secondary);
  border-bottom: 1px solid var(--color-border);
  transition: background-color 0.3s;
}

.chapter-lessons-articles a {
  display: block;
  padding: var(--padding-base);
  text-decoration: none;
  color: var(--color-secondary);
  border-bottom: 1px solid var(--color-border);
  transition: background-color 0.3s;
}

.chapter-lessons-preps a:last-child {
  border-bottom: none;
}

.chapter-lessons-articles a:last-child {
  border-bottom: none;
}

.chapter-lessons-preps a:hover {
  background-color: var(--color-background);
}


.chapter-lessons-articles a:hover {
  background-color: var(--color-background);
}

/* CLEANUP: 
  Replaced .chapter-lessons-preps and .chapter-lessons-articles 
  with one generic .chapter-lessons class to match the new index.html
*/
.chapter-lessons {
  display: none;
  border-top: 1px solid var(--color-border);
}

.chapter-lessons a {
  display: block;
  padding: var(--padding-base);
  text-decoration: none;
  color: var(--color-secondary);
  border-bottom: 1px solid var(--color-border);
  transition: background-color 0.3s;
}

.chapter-lessons a:last-child {
  border-bottom: none;
}

.chapter-lessons a:hover {
  background-color: var(--color-background);
}

.site-footer {
  text-align: center;
  padding: var(--padding-base);
  font-size: var(--font-size-base);
  border-top: 1px solid var(--color-border);
  margin-top: var(--margin-base);
  background-color: var(--color-body-bg);
}

/* Lessons' styles (for verbs_memorize.html, verbs_practice.html, etc.) */
.interactive-page .container {
  max-width: var(--max-width-lesson);
 }

.exercise-header {
  text-align: center;
  margin-bottom: var(--margin-base);
}

.exercise-header h2 {
  font-size: var(--font-size-large);
  color: var(--color-primary);
  margin-bottom: 8px;
}

.progress {
  font-size: var(--font-size-base);
  color: var(--color-secondary);
}

/* Question area */
.question-card {
  background-color: var(--color-body-bg);
  border: 1px solid var(--color-border);
  border-radius: 4px;
  padding: var(--padding-base);
  margin-bottom: var(--margin-base);
  min-height: 200px;
}

#answer_text_field {
  width: 100%;
  padding: 8px;
  font-size: var(--font-size-base);
  border: 1px solid var(--color-border);
  border-radius: 4px;
  margin-bottom: var(--margin-base);
}

.result-section {
  text-align: center;
  margin-bottom: var(--margin-base);
  font-size: var(--font-size-base);
}

.button-group {
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  gap: var(--margin-base);
  margin-bottom: var(--margin-base);
}

.button-group button {
  padding: 10px 20px;
  font-size: var(--font-size-base);
  border: none;
  background-color: var(--color-secondary);
  color: #fff;
  border-radius: 4px;
  cursor: pointer;
  transition: background-color 0.3s ease;
}


.button-group button:hover {
  background-color: var(--color-primary);
}

/* Preferred button variant (from borrowed CSS) */
.button-group button.preferred {
  background-color: var(--color-preferred);
}

.button-group button.preferred:hover {
  background-color: var(--color-primary);
}

.back-link {
  text-align: center;
  margin-top: var(--margin-base);
}

.back-link a {
  text-decoration: none;
  color: var(--color-secondary);
  font-weight: bold;
}

.correct {
  color: var(--color-success);
}

.wrong {
  color: var(--color-error);
}

/* Grid , cells no margin */
.answer-options {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(120px, 1fr));
  gap: var(--margin-base);
  margin-bottom: var(--margin-base);
}

.answer-options > *:hover {
  background-color: var(--color-background);
}


/* hiding radio-input */
#answer_radiobutton_div input[type="radio"] {
  opacity: 0;
  position: absolute;
  pointer-events: none;
}

/* radio-input-like label */
#answer_radiobutton_div label {
  flex-grow: 1;
  flex-shrink: 0;
  background-color: var(--color-body-bg);
  border: 1px solid var(--color-border);
  padding: var(--padding-base);
  text-align: center;
  cursor: pointer;
  transition: all 0.3s ease-in-out;

  display: block;
  position: relative;
  cursor: pointer;
  user-select: none;
  font-size: var(--font-size-medium);
  color: var(--color-text);
}


/* when input is checked label is colored */
#answer_radiobutton_div input[type="radio"]:checked + label {
  background-color: var(--color-secondary);
  color: var(--color-body-bg);
}

#answer_radiobutton_div label:hover {
  border-color: var(--color-secondary);
}

#answer_radiobutton_div label:active {
  transform: scale(0.98);
}

/* Styles for info/grammar pages (from borrowed CSS) */
.info-page .container {
  max-width: var(--max-width-lesson);
}

#spnTopic {
  display: block;
  text-align: center;
  font-size: var(--font-size-large);
  color: var(--color-primary);
  margin-bottom: 8px;
  font-weight: 600;
}

#spnGrammar {
  display: block;
  text-align: left;
  color: var(--color-text);
  margin-bottom: var(--margin-base);
  font-size: var(--font-size-base);
  line-height: 1.6;
}

#spnGrammar br {
  display: block;
  margin-bottom: 0.6em;
  content: "";
}

.grammar-card {
  background-color: var(--color-body-bg);
  border: 1px solid var(--color-border);
  border-radius: 4px;
  padding: var(--padding-base);
  margin-bottom: var(--margin-base);
}

.info-page .back-link {
  text-align: center;
  margin-top: var(--margin-base);
}

.info-page .back-link a {
  text-decoration: none;
  color: var(--color-secondary);
  font-weight: bold;
}

.info-page .back-link a:hover {
  text-decoration: underline;
}


/* desktop handling */
@media (min-width: 768px) {
  .container {
    padding: calc(var(--padding-base) * 1.5);
  }
  .chapter-header {
    padding: calc(var(--padding-base) * 1.5);
  }

  /* CLEANUP: Pointing this to the generic .chapter-lessons class */
  .chapter-lessons a {
    padding: calc(var(--padding-base) * 1.25);
  }
  .exercise-header h2 {
    font-size: calc(var(--font-size-large) * 1.1);
  }
  #spnTopic {
    font-size: calc(var(--font-size-large) * 1.1);
  }
}