:root {
            /* Hydration Palette */
            --hydration-primary: #00b4d8;    /* Aqua/Cyan */
            --hydration-primary-dark: #2D9D78; /* Deeper Blue */
            --hydration-primary-light: #90e0ef; /* Lighter Cyan */
            --hydration-secondary: #48cae4;  /* Sky Blue */
            --hydration-secondary-dark: #023e7d; /* Dark Blue */
            --hydration-secondary-light: #ade8f4; /* Pale Blue */
            --hydration-accent: #99e2b4;     /* Mint Green */
            --hydration-accent-dark: #70e000; /* Vibrant Green */

            /* Neutrals (Can borrow or adjust slightly) */
            --neutral-light: #f3f4f6;
            --neutral: #e5e7eb;
            --neutral-dark: #9ca3af;
            --text-dark: #1f2937;
            --text-light: #6b7280;
        }

        body {
            font-family: 'Inter', system-ui, -apple-system, sans-serif;
            color: var(--text-dark);
            background-color: #e0f7fa; /* Very light blue background */
            overflow-x: hidden;
        }

        .container {
            max-width: 1200px;
            margin: 0 auto;
        }

         .header {
            background: linear-gradient(135deg, var(--hydration-primary-dark), var(--hydration-secondary-dark)); /* Deep blue gradient */
            color: white;
            padding: 2rem 0;
            position: relative;
            overflow: hidden;
        }

        .header::before {
            content: '';
            position: absolute;
            width: 100%;
            height: 100%;
            top: 0;
            left: 0;
             background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 1440 320'%3E%3Cpath fill='%23ffffff' fill-opacity='0.15' d='M0,160L48,176C96,192,192,224,288,218.7C384,213,480,160,576,133.3C672,107,768,107,864,133.3C960,160,1056,213,1152,213.3C1248,213,1344,160,1392,133.3L1440,107L1440,320L1392,320C1344,320,1248,320,1152,320C1056,320,960,320,864,320C768,320,672,320,576,320C480,320,384,320,288,320C192,320,96,320,48,320L0,320Z'%3E%3C/path%3E%3C/svg%3E"); /* Watery wave */
            background-size: cover;
            opacity: 0.2; /* Slightly more visible pattern */
            pointer-events: none;
        }

        .calculator-card, .info-card {
            background-color: white;
            border-radius: 1.5rem; /* More rounded corners */
            box-shadow: 0 10px 15px -3px rgba(0, 0, 0, 0.1), 0 4px 6px -2px rgba(0, 0, 0, 0.05);
            transition: all 0.3s ease;
            overflow: hidden; /* Ensure gradients stay within */
        }

         .calculator-card {
             border-left: none; /* No left border */
             background: linear-gradient(180deg, #ffffff 95%, var(--hydration-primary-light) 100%); /* Subtle gradient at bottom */
         }

        .info-card {
            border-left: 4px solid var(--hydration-primary); /* Use primary hydration color */
        }


        input[type="number"], select, input[type="radio"] + label {
            border: 1px solid var(--neutral); /* Thinner border */
            border-radius: 0.75rem; /* More rounded input */
            padding: 0.85rem 1.2rem; /* Slightly more padding */
            transition: all 0.3s ease;
            width: 100%;
             box-sizing: border-box;
             background-color: var(--neutral-light); /* Light background in inputs */
        }

         input[type="number"]:focus, select:focus {
            outline: none;
            border-color: var(--hydration-primary); /* Hydration primary color on focus */
            box-shadow: 0 0 0 4px var(--hydration-primary-light); /* Lighter shadow */
             background-color: white; /* White background on focus */
        }

        .input-group {
             display: flex;
             align-items: center;
        }

         .input-group input {
             flex-grow: 1; /* Allow input to take available space */
             margin-right: 0.75rem; /* Space between input and units */
         }

        .btn-toggle {
            background-color: var(--neutral-light);
            color: var(--text-light);
            border-radius: 0.75rem; /* More rounded toggle buttons */
            padding: 0.6rem 1.2rem; /* Adjusted padding */
            font-weight: 500;
            transition: all 0.3s ease;
            cursor: pointer;
             border: 1px solid var(--neutral); /* Border for toggles */
        }

        .btn-toggle.active {
             background-color: var(--hydration-primary); /* Primary hydration color */
            color: white;
            font-weight: 600;
             border-color: var(--hydration-primary);
        }

        .primary-btn {
            background: linear-gradient(90deg, var(--hydration-primary), var(--hydration-secondary)); /* Gradient button */
            color: white;
            border-radius: 0.75rem; /* More rounded button */
            padding: 0.9rem 2rem; /* Larger padding */
            font-size: 1.125rem; /* Slightly larger text */
            font-weight: 700; /* Bolder text */
            transition: all 0.3s ease;
            border: none;
            cursor: pointer;
            position: relative; /* For potential ripple effect */
            overflow: hidden; /* For potential ripple effect */
        }

        .primary-btn:hover {
            background: linear-gradient(90deg, var(--hydration-primary-dark), var(--hydration-secondary-dark));
            transform: translateY(-3px); /* More pronounced lift */
            box-shadow: 0 8px 15px rgba(0, 0, 0, 0.2); /* Added shadow on hover */
        }

        .primary-btn:active {
            transform: translateY(0);
            box-shadow: none;
        }

        /* Radio button styling */
        .radio-container {
            display: block;
            position: relative;
            padding-left: 35px;
            margin-bottom: 12px;
            cursor: pointer;
            font-size: 16px;
            user-select: none;
        }

        .radio-container input {
            position: absolute;
            opacity: 0;
            cursor: pointer;
            height: 0;
            width: 0;
        }

        .radiomark {
            position: absolute;
            top: 0;
            left: 0;
            height: 24px;
            width: 24px;
            background-color: var(--neutral-light);
            border-radius: 50%;
            transition: all 0.2s ease;
            border: 1px solid var(--neutral); /* Border for radiomark */
        }

        .radio-container:hover input ~ .radiomark {
            background-color: var(--neutral);
        }

        .radio-container input:checked ~ .radiomark {
            background-color: var(--hydration-primary); /* Primary hydration color */
            border-color: var(--hydration-primary);
        }

        .radiomark:after {
            content: "";
            position: absolute;
            display: none;
        }

        .radio-container input:checked ~ .radiomark:after {
            display: block;
        }

        .radio-container .radiomark:after {
            top: 6px; /* Slightly larger dot */
            left: 6px;
            width: 10px; /* Slightly larger dot */
            height: 10px;
            border-radius: 50%;
            background: white;
        }


        .result-section {
             background: linear-gradient(180deg, var(--hydration-secondary-light), var(--hydration-primary-light)); /* Light gradient */
            border-radius: 1.5rem;
            overflow: hidden;
            transition: all 0.6s ease-out; /* Slower, smoother transition */
            opacity: 0;
            max-height: 0;
        }

        .result-section.show {
            opacity: 1;
            max-height: 2000px; /* Adjust as needed for content height */
            margin-top: 2.5rem; /* Slightly more space */
        }

        .hydration-icon {
             width: 60px;
             height: 60px;
             background-color: var(--hydration-primary-light);
             border-radius: 50%;
             display: flex;
             align-items: center;
             justify-content: center;
             margin-right: 1rem;
        }

         .hydration-icon i {
            color: var(--hydration-primary-dark);
            font-size: 30px;
         }

        /* Hydration result specific styles */
        .fluid-amount {
            font-size: 3.5rem; /* Larger font */
            font-weight: 800; /* Extra bold */
            color: var(--hydration-primary-dark); /* Dark primary color */
            line-height: 1; /* Tighter line height */
        }

        .fluid-unit {
             font-size: 1.5rem;
             color: var(--text-dark);
             font-weight: 600;
             margin-left: 0.5rem;
        }

        .hydration-visual {
             position: relative;
             width: 100%;
             height: 200px; /* Fixed height for the visual */
             background-color: var(--neutral-light);
             border-radius: 1rem;
             overflow: hidden;
             margin-bottom: 1.5rem;
        }

         .hydration-visual .fluid-level {
             position: absolute;
             bottom: 0;
             left: 0;
             width: 100%;
             height: 0%; /* Start at 0 */
             background: linear-gradient(0deg, var(--hydration-primary), var(--hydration-secondary)); /* Fluid gradient */
             transition: height 2s ease-out; /* Animated fill */
             border-top-left-radius: 0.5rem;
             border-top-right-radius: 0.5rem;
         }

         .hydration-visual .fluid-label {
             position: absolute;
             top: 50%;
             left: 50%;
             transform: translate(-50%, -50%);
             font-size: 1.5rem;
             font-weight: 700;
             color: white;
             text-shadow: 1px 1px 3px rgba(0,0,0,0.3);
             mix-blend-mode: overlay; /* Blend text with background */
             opacity: 0; /* Initially hidden */
             transition: opacity 1s ease 1s; /* Fade in after fill */
         }
         .result-section.show .hydration-visual .fluid-label {
             opacity: 1;
         }


        /* Theory sections */
        .theory-section .info-card {
            border-left: 4px solid var(--hydration-accent); /* Accent color for theory */
        }

         .theory-section .info-card .bx {
             color: var(--hydration-accent-dark); /* Dark accent color for theory icons */
         }


        /* Athlete icons */
        .athlete-icons {
            position: relative;
            height: 300px;
        }

        .athlete-icon {
            position: absolute;
            width: 60px;
            height: 60px;
            background-color: var(--hydration-secondary-light); /* Secondary light hydration color */
            border-radius: 50%;
            display: flex;
            align-items: center;
            justify-content: center;
             animation: ripple 2s ease-in-out infinite; /* Different animation */
        }

         @keyframes ripple {
             0%, 100% {
                 transform: scale(1);
                 opacity: 1;
             }
             50% {
                 transform: scale(1.1);
                 opacity: 0.8;
             }
         }


        .athlete-icon:nth-child(1) { top: 20%; left: 10%; animation-delay: 0s; }
        .athlete-icon:nth-child(2) { top: 60%; left: 20%; animation-delay: 0.3s; }
        .athlete-icon:nth-child(3) { top: 30%; left: 35%; animation-delay: 0.6s; }
        .athlete-icon:nth-child(4) { top: 50%; left: 55%; animation-delay: 0.9s; }
        .athlete-icon:nth-child(5) { top: 25%; left: 75%; animation-delay: 1.2s; }
        .athlete-icon:nth-child(6) { top: 65%; left: 85%; animation-delay: 1.5s; }


        .athlete-icon i {
            font-size: 30px;
            color: var(--hydration-secondary-dark); /* Dark secondary hydration color */
        }

         /* Custom styles for header graphics */
        .header-graphics {
            position: absolute;
            top: 0;
            right: 0;
            width: 100%;
            height: 100%;
            overflow: hidden;
            pointer-events: none;
        }

        .header-graphic {
            position: absolute;
            opacity: 0.2; /* More visible graphics */
             color: white; /* Set color for graphics */
        }

        .header-graphic.water-drop {
            top: 10%; right: 5%; font-size: 4rem; animation: float-drop 4s ease-in-out infinite;
        }
         .header-graphic.sweat-drop {
             bottom: 15%; right: 20%; font-size: 3.5rem; animation: float-drop 4s ease-in-out infinite 0.5s;
         }
        .header-graphic.bottle {
            top: 20%; left: 10%; font-size: 3.5rem; transform: rotate(-15deg); animation: float 3s ease-in-out infinite 0.2s;
        }
        .header-graphic.sun {
             bottom: 10%; left: 20%; font-size: 3rem; animation: rotate-float 5s linear infinite;
        }
         .header-graphic.clock {
             top: 30%; right: 30%; font-size: 3rem; animation: float 3.5s ease-in-out infinite 0.8s;
         }

         @keyframes float-drop {
             0% { transform: translateY(0px); }
             50% { transform: translateY(-15px); }
             100% { transform: translateY(0px); }
         }

        @keyframes rotate-float {
             0% { transform: translateY(0px) rotate(0deg); }
             50% { transform: translateY(-10px) rotate(180deg); }
             100% { transform: translateY(0px) rotate(360deg); }
        }


        /* Tooltip styles */
        .tooltip {
            position: relative;
            display: inline-block;
            cursor: pointer;
        }

        .tooltip .tooltiptext {
            visibility: hidden;
            width: 200px;
            background-color: var(--text-dark);
            color: white;
            text-align: center;
            border-radius: 6px;
            padding: 10px;
            position: absolute;
            z-index: 1;
            bottom: 125%;
            left: 50%;
            transform: translateX(-50%);
            opacity: 0;
            transition: opacity 0.3s;
            font-size: 0.875rem;
        }

        .tooltip .tooltiptext::after {
            content: "";
            position: absolute;
            top: 100%;
            left: 50%;
            margin-left: -5px;
            border-width: 5px;
            border-style: solid;
            border-color: var(--text-dark) transparent transparent transparent;
        }

        .tooltip:hover .tooltiptext {
            visibility: visible;
            opacity: 1;
        }


        /* Responsive Adjustments */
        @media (max-width: 768px) {
            .header h1 {
                font-size: 1.75rem;
            }

            .athlete-icons {
                height: 150px; /* Reduced height */
            }

            .athlete-icon {
                width: 35px; /* Smaller icons */
                height: 35px;
            }

            .athlete-icon i {
                font-size: 18px;
            }

            .fluid-amount {
                font-size: 2.5rem; /* Smaller font on mobile */
            }

             .fluid-unit {
                 font-size: 1.2rem;
             }

             .hydration-visual {
                 height: 150px; /* Reduced height on mobile */
             }
              .hydration-visual .fluid-label {
                 font-size: 1rem;
              }
        }

         /* For smooth scrolling */
        html {
            scroll-behavior: smooth;
        }

        footer {
            background-color: var(--text-dark);
            color: white;
            padding: 2rem 0;
            margin-top: 3rem;
        }