:root {
  --navy: #2c3e50;
  --softgray: #ecf0f1;
  --teal: #1abc9c;
  --gold: #f1c40f;
  --slate: #7f8c8d;
  --coral: #e74c3c;
  --white: #ffffff;
  --gray-100: #f7fafc;
  --gray-200: #edf2f7;
  --gray-300: #e2e8f0;
  --max-width: 1120px;
  --container-pad: 16px;
  --radius: 10px;
  --shadow-sm: 0 6px 18px rgba(0, 0, 0, 0.06);
  --shadow-xs: 0 1px 2px rgba(0, 0, 0, 0.06);
}

* {
  box-sizing: border-box;
}

html,
body {
  height: 100%;
}

body {
  margin: 0;
  font-family: "Montserrat", system-ui, -apple-system, "Segoe UI", Roboto,
    "Helvetica Neue", Arial;
  color: var(--navy);
  background: linear-gradient(135deg, #ecf0f1 0%, #d6dbdf 100%);
  padding: 16px 16px 80px;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}
li {
  line-height: 2; 
}

/* Page header */
.header-left{
  justify-self: start;
}

.page-header {
    text-align: center;
    color: var(--navy);
    padding: 1rem;
    position: relative;
}

.header-grid{
  display: grid;
  grid-template-columns: 1fr auto 1fr; 
  align-items: center;
  gap: 12px;
  padding: 8px 0;
}
.page-title{
  margin: 0;
  justify-self: center;   /* ensures exact centering of the title cell */
  font-size: 2rem;
  font-weight: 700;
  font-family: 'Montserrat', sans-serif;
}
.header-actions{
  justify-self: end;
}

/* mobile: stack nicely */
@media (max-width: 767px){
  .header-grid{
    grid-template-columns: 1fr; /* stack everything */
    grid-auto-flow: row;
    text-align: left;
  }
  .page-title{ justify-self: start; }
  .header-actions{ justify-self: start; width:100%; margin-top:8px; }
  
}
.cols {
  display: flex;
  flex-direction: column;
  gap: 24px;
}

/* center the title inside the middle column */
.page-title{
  margin: 0;
  justify-self: center;   /* ensures exact centering of the title cell */
  font-size: 2rem;
  font-weight: 700;
  font-family: 'Montserrat', sans-serif;
}

/* position actions at the end of the right column */
.header-actions{
  justify-self: end;
}

/* mobile: stack nicely */
@media (max-width: 767px){
  .header-grid{
    grid-template-columns: 1fr; /* stack everything */
    grid-auto-flow: row;
    text-align: left;
  }
  .page-title{ justify-self: start; }
  .header-actions{ justify-self: start; width:100%; margin-top:8px; }
  .quiz-btn{ width:100%; max-width:420px; }
}


.experiment-container {
  background: white;
    border-radius: 12px;
    box-shadow: 0 4px 12px rgba(0,0,0,0.08);
    padding: 30px;
    max-width: 1000px;
    margin: 30px auto;
    border: 1px solid #eaeaea;
   margin-top: 5px; 
  
    display: flex;
    justify-content: space-around;
    
   
   flex-direction: row; /* Default horizontal layout */
    flex-wrap: wrap; /* Allow wrapping */
    gap: 20px; /* Space between items */
    
}

.test-tube {
    position: relative;
   width: calc(25% - 20px); /* 4 tubes per row on large screens */
    min-width: 150px; /* Minimum width */
    margin-bottom: 30px;
    padding-top:180px;
    display: flex;
    flex-direction: column;
    align-items: center;
}

.tube-body {
    width: 40px;
    height: 150px;
    border-radius: 0 0 40px 40px;
    position: relative;
    overflow: hidden;
    border: 2px solid #333;
    border-top: none;
    
}



.thermometer {
    position: absolute;
    width: 8px;
    height: 200px;
  
    background-color: #fff;
    border: 1px solid #333;
    border-radius: 4px;
    left: 50%;
    transform: translateX(-50%);
    margin-top: -120px;
    z-index: 0;
}

.mercury {
    position: absolute;
    bottom: 5px;
    left: 1px;
    width: 6px;
    background-color: #e74c3c;
    border-radius: 3px;
    transition: height 1s linear;
}

.temperature-display {
    margin-top: 10px;
    font-weight: bold;
    font-size: 18px;
}

.controls {
  margin: 30px auto 80px;
  display: flex;
  justify-content: center; /* Center the buttons horizontally */
  flex-wrap: wrap; /* Allow wrapping if needed */
  gap: 10px; /* Space between buttons */
}

/* Button styles */
.teal-btn {
  background-color: rgba(26, 188, 156, 0.8);
  color: white;
}

.teal-btn:hover {
    background-color: rgba(26, 188, 156, 0.7);
    transform: translateY(-2px);
}

.gold-btn {
  background-color: rgba(241, 196, 15, 1);
  color: var(--navy); opacity:0.9;
}

.gold-btn:hover {
  background-color: rgba(241, 196, 15, 0.5);
  transform: translateY(-2px);
}

.coral-btn {
  background-color: rgba(231, 76, 60, 0.8);
  color: white;
}

.coral-btn:hover {
  background-color: rgba(231, 76, 60, 0.7);
  transform: translateY(-2px);
}

.navy-btn {
  background-color: rgba(44, 62, 80, 0.8);
  color: white;
}

.navy-btn:hover {
    background-color: rgba(44, 62, 80, 0.7);
    transform: translateY(-2px);
}
.button-stack {
  display: flex;
  flex-direction: column;
  gap: 10px;
  margin-top: 24px;
}

.btn {
    display: inline-block;
    padding: 0.5rem 1rem;
    border-radius: 0.375rem;
    font-weight: 500;
    text-decoration: none;
    text-align: center;
    transition: all 0.2s;
    cursor: pointer;
    border: 1px solid transparent;
    width: auto;
    font-size: 16px;
    font-weight: 600;
    padding: 12px 24px;
}

#stopwatch {
  font-family: 'Courier New', monospace;
  font-size: 1.8rem;
  background: #2c3e50;
  color: white;
  padding: 10px 20px;
  border-radius: 6px;
  display: block; /* Change from inline-block to block */
  margin: 20px auto; /* Center horizontally with auto margins */
  letter-spacing: 2px;
  text-align: center; /* Center the text inside */
  width: fit-content; /* Or set a specific width like 200px */
}

/* Tube colors */
.black { background-color: #333 !important; }
.white { background-color: #fff !important; }
.silver { background-color: #c0c0c0 !important; background-image: linear-gradient(to right, #c0c0c0, #e0e0e0, #c0c0c0) !important; }
.clear { background-color: rgba(200, 200, 255, 0.3) !important; }

#help-button{
  position: fixed;
  border: none;
  color: white;
  top: 20px;
  left: 20px;
  background-color: #3498db;
  text-align: center;
  text-decoration: none;
  display: inline-block;
  font-size: 16px;
  width: 40px;
   height: 40px;
  
}



/* Media queries for different screen sizes */
@media (max-width: 1024px) { /* Tablet landscape */
    .test-tube {
        width: calc(33% - 20px); /* 3 tubes per row */
    }
}

@media (max-width: 768px) { /* Tablet portrait */
    .test-tube {
        width: calc(50% - 20px); /* 2 tubes per row */
    }
    
    .experiment-container {
        justify-content: center; /* Center tubes */
    }
}

@media (max-width: 480px) { /* Mobile */
    .test-tube {
        width: 100%; /* 1 tube per row */
        max-width: 200px;
    }
   .controls {
        display: flex;
        flex-direction: column;
        gap: 10px;
    }
    
    button {
        width: 100%;
    }
}

.controls-wrapper {
  margin-bottom: 20px;
  width: 100%;
  display: flex;
  justify-content: center;
}

/* Instructions + Results panels */
.panel {
  max-width: 1000px;
  margin: 20px auto;
  background: white;
  border-radius: 8px;
  padding: 16px;
  box-shadow: var(--shadow-sm);
}

.panel h3 {
  margin: 0 0 12px 0;
  font-size: 18px;
}

.panel-body {
  font-size: 14px;
  line-height: 1.6;
}

.instructions-aim {
  margin: 0 0 12px 0;
}

/* Results table */
.table-wrap {
  overflow-x: auto;
}

.results-table {
  width: 100%;
  border-collapse: collapse;
  background: white;
  border: 1px solid var(--softgray);
}

.results-table th,
.results-table td {
  border: 1px solid var(--softgray);
  padding: 8px;
  text-align: left;
}

.results-table thead tr {
  background: var(--softgray);
}

.results-table th {
  font-weight: 700;
}

.table-input {
  width: 100%;
  max-width: 120px;
  padding: 8px;
  border-radius: 6px;
  border: 1px solid var(--gray-300);
  background: white;
  font: inherit;
  color: var(--navy);
  text-align: center;
}

.table-input:focus {
  outline: 3px solid rgba(26, 188, 156, 0.18);
  outline-offset: 2px;
}

.text-center {
  text-align: center;
}

.row-delete {
  background: none;
  border: 0;
  cursor: pointer;
  color: #e53e3e;
  font-size: 16px;
}