feat: добавлена светлая тема с кнопкой переключения

frontend/style.css

@@ -27,6 +27,33 @@
   --transition: 0.25s cubic-bezier(0.4, 0, 0.2, 1);
 }
 
+/* ===== Light Theme ===== */
+[data-theme="light"] {
+  --bg-primary: #e8eaef;
+  --bg-card: rgba(255, 255, 255, 0.95);
+  --bg-card-border: rgba(0, 0, 0, 0.22);
+  --bg-input: rgba(0, 0, 0, 0.08);
+  --bg-input-focus: rgba(0, 0, 0, 0.12);
+  --text-primary: #0f172a;
+  --text-secondary: #374151;
+  --text-placeholder: #6b7280;
+  --accent: #6366f1;
+  --accent-hover: #4f46e5;
+  --accent-glow: rgba(99, 102, 241, 0.25);
+  --error: #dc2626;
+  --success: #16a34a;
+}
+
+[data-theme="light"] .shape {
+  opacity: 0.25;
+}
+
+[data-theme="light"] .login-card {
+  box-shadow:
+    0 8px 32px rgba(0, 0, 0, 0.08),
+    inset 0 1px 0 rgba(255, 255, 255, 0.6);
+}
+
 html {
   font-size: 16px;
   -webkit-font-smoothing: antialiased;
@@ -42,6 +69,7 @@ body {
   align-items: center;
   justify-content: center;
   overflow: hidden;
+  transition: background 0.4s ease, color 0.4s ease;
 }
 
 /* ===== Animated Background ===== */
@@ -58,6 +86,7 @@ body {
   filter: blur(80px);
   opacity: 0.5;
   animation: float 20s ease-in-out infinite;
+  transition: opacity 0.4s ease;
 }
 
 .shape-1 {
@@ -89,10 +118,23 @@ body {
 }
 
 @keyframes float {
-  0%, 100% { transform: translate(0, 0) scale(1); }
-  25% { transform: translate(30px, -40px) scale(1.05); }
-  50% { transform: translate(-20px, 20px) scale(0.95); }
-  75% { transform: translate(15px, 35px) scale(1.03); }
+
+  0%,
+  100% {
+    transform: translate(0, 0) scale(1);
+  }
+
+  25% {
+    transform: translate(30px, -40px) scale(1.05);
+  }
+
+  50% {
+    transform: translate(-20px, 20px) scale(0.95);
+  }
+
+  75% {
+    transform: translate(15px, 35px) scale(1.03);
+  }
 }
 
 /* ===== Login Container ===== */
@@ -110,6 +152,7 @@ body {
     opacity: 0;
     transform: translateY(24px);
   }
+
   to {
     opacity: 1;
     transform: translateY(0);
@@ -127,6 +170,7 @@ body {
   box-shadow:
     0 8px 32px rgba(0, 0, 0, 0.3),
     inset 0 1px 0 rgba(255, 255, 255, 0.05);
+  transition: background 0.4s ease, border-color 0.4s ease, box-shadow 0.4s ease;
 }
 
 /* ===== Header ===== */
@@ -142,8 +186,15 @@ body {
 }
 
 @keyframes pulse-glow {
-  0%, 100% { filter: drop-shadow(0 0 6px var(--accent-glow)); }
-  50% { filter: drop-shadow(0 0 18px var(--accent-glow)); }
+
+  0%,
+  100% {
+    filter: drop-shadow(0 0 6px var(--accent-glow));
+  }
+
+  50% {
+    filter: drop-shadow(0 0 18px var(--accent-glow));
+  }
 }
 
 .login-header h1 {
@@ -214,8 +265,8 @@ body {
   box-shadow: 0 0 0 3px var(--accent-glow);
 }
 
-.input-wrapper input:focus ~ .input-icon,
-.input-wrapper input:focus + .input-icon {
+.input-wrapper input:focus~.input-icon,
+.input-wrapper input:focus+.input-icon {
   color: var(--accent);
 }
 
@@ -320,7 +371,9 @@ body {
 }
 
 @keyframes spin {
-  to { transform: rotate(360deg); }
+  to {
+    transform: rotate(360deg);
+  }
 }
 
 /* ===== Input Error State ===== */
@@ -329,6 +382,47 @@ body {
   box-shadow: 0 0 0 3px rgba(248, 113, 113, 0.15);
 }
 
+/* ===== Theme Toggle Button ===== */
+.theme-toggle {
+  width: 42px;
+  height: 42px;
+  border: none;
+  border-radius: 50%;
+  background: var(--bg-card);
+  border: 1px solid var(--bg-card-border);
+  color: var(--text-primary);
+  cursor: pointer;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  backdrop-filter: blur(12px);
+  -webkit-backdrop-filter: blur(12px);
+  transition: background 0.3s ease, transform 0.3s ease, box-shadow 0.3s ease;
+  z-index: 100;
+  flex-shrink: 0;
+}
+
+.theme-toggle svg {
+  width: 20px;
+  height: 20px;
+  transition: transform 0.4s ease;
+}
+
+.theme-toggle:hover {
+  transform: scale(1.1);
+  box-shadow: 0 4px 16px var(--accent-glow);
+}
+
+.theme-toggle:active {
+  transform: scale(0.95);
+}
+
+.theme-toggle--fixed {
+  position: fixed;
+  top: 1.25rem;
+  right: 1.25rem;
+}
+
 /* ===== Responsive ===== */
 @media (max-width: 480px) {
   .login-card {
@@ -338,4 +432,16 @@ body {
   .login-header h1 {
     font-size: 1.3rem;
   }
-}
+
+  .theme-toggle--fixed {
+    top: 0.75rem;
+    right: 0.75rem;
+    width: 36px;
+    height: 36px;
+  }
+
+  .theme-toggle--fixed svg {
+    width: 18px;
+    height: 18px;
+  }
+}